Histopathology 2016, 68, 398–404. DOI: 10.1111/his.12755
Clinicopathological and immunohistological features of polypoid endometriosis Colin JR Stewart1,2 & Chrianna Bharat3,4 1
Department of Pathology, King Edward Memorial Hospital, 2School of Women’s and Infants’ Health, 3Centre for Applied Statistics, University of Western Australia, and 4Department of Research, Sir Charles Gairdner Hospital, Perth, WA, Australia
Date of submission 5 May 2015 Accepted for publication 5 June 2015 Published online Article Accepted 10 June 2015
Stewart C JR & Bharat C (2016) Histopathology 68, 398–404. DOI: 10.1111/his.12755
Clinicopathological and immunohistological features of polypoid endometriosis Aims: To compare clinicopathological and immunohistochemical features of polypoid endometriosis (PE) and non-polypoid endometriosis (NPE). Methods and results: Fifteen cases of PE and 20 cases of NPE were assessed. All cases were stained immunohistochemically for CD10 and p16 and the proportion of p16-positive stromal and epithelial cells was estimated. On review, 10 PE cases resembled NPE histologically but occurred at mucosal or serosal surfaces, or within cyst cavities, that permitted polyp formation. These cases had a similar age distribution and immunohistochemical profile to NPE. The remaining five PE cases showed histological similarity
to eutopic endometrial polyps; these occurred in older patients, and showed significantly greater stromal and epithelial p16 immunoreactivity. Conclusions: There are two main subgroups of PE. The majority of cases in this series showed similar histological features to NPE, but involved anatomical sites that facilitated exophytic or polypoid growth. The remaining PE cases resembled eutopic endometrial polyps histologically and immunophenotypically and they occurred in older patients. These findings suggest that such lesions are ‘true’ polyps sharing a pathogenetic relationship with similar lesions arising in the endometrium.
Keywords: endometrial polyp, endometriosis, immunohistochemistry, polypoid, p16
Introduction Endometriosis, defined as the presence of endometriotic glandular and stromal tissue outside the uterine corpus, is one of the most common gynaecological pathological processes, being identified in 10–15% of all women.1 While the diagnosis of endometriosis is usually straightforward, pathologists need to be aware of the many histological variants of this common condition, some of which can present diagnostic difficulty.2 One interesting variant is so-called polypoid endometriosis (PE), which has been the subject of only one detailed study.3 To the best of our
Address for correspondence: C JR Stewart, Department of Histopathology, King Edward Memorial Hospital, Bagot Road, Perth, WA 6008, Australia. e-mail: [email protected] © 2015 John Wiley & Sons Ltd.
knowledge, the term PE (or ‘endometriotic polyposis’) was introduced by Mostoufizadeh and Scully for cases of endometriosis which resembled an endometrial polyp microscopically.4 In their series, Parker et al. broadened the term to include cases of endometriosis that were simply polypoid from the gross aspect.3 In this study we present a series of 15 cases of cases of PE, including cases that fit the original stricter definition of Mostoufizadeh and Scully,4 but additionally cases that met the broader criteria of Parker et al.4 to investigate further the differing clinical and microscopic aspects of these two forms of endometriosis. Because recent studies have suggested that stromal cell p16 expression is characteristic of (eutopic) endometrial polyps,5,6 we also compared CD10 and p16 immunoreactivity in these lesions, and in a series of conventional (non-polypoid) endometriotic lesions.
Polypoid endometriosis
399
The specimens were obtained from the histopathology files of King Edward Memorial Hospital, Perth. All samples were fixed in buffered formalin and processed routinely to paraffin wax. Serial 4-l sections were stained with haematoxylin and eosin (H&E) and immunohistochemically, as described below. Two main groups of cases were investigated, conventional or non-polypoid endometriosis (NPE) and PE. Patient age and the histological appearances of the endometrium, when available, were recorded. Details of hormonal therapy were not available in these cases. The study received institutional ethics approval (KEMH reference 8567).
present, to some extent mimicking normal endometrium. Second were those cases where the glandular and stromal appearances resembled more closely those seen in eutopic endometrial polyps (designated group 2). In these cases the glands typically exhibited a range in calibre, often with focal cystic change, and the lining epithelium frequently demonstrated metaplastic alterations (mucinous, ciliated and/or eosinophilic). The stroma included plump, ovoid- to spindle-shaped cells which were separated by a relatively abundant, mature collagenous matrix. Thickwalled blood vessels, characteristic of eutopic endometrial polyps, were not a prominent feature of either type of PE in this series.
NON-POLYPOID ENDOMETRIOSIS
IMMUNOHISTOCHEMISTRY
Twenty-two biopsy or resection specimens from 20 patients were examined. These were selected randomly from cases encountered over a 2-year period to demonstrate endometriosis occurring in a variety of anatomical sites. The sites comprised pelvic peritoneum including the uterine serosa (n = 5), ovary (n = 4), colorectum and vagina (both n = 3), appendix, fallopian tube and ureter (all n = 2) and pelvic lymph node (n = 1).
Immunohistochemistry for p16 protein and CD10 was performed as described previously.6,7 Immunostaining for p16 was assessed separately within the epithelial and stromal components, and the percentage of positive cells was estimated to the closest 10%.6 As staining intensity was strong in all positive cases, this was not recorded separately. For the two NPE cases with two samples the average staining percentage was used in the analysis.
Materials and methods
POLYPOID ENDOMETRIOSIS
Fifteen consecutive cases of PE identified by one author (C.J.R.S.) during a 5-year period were studied. As defined previously,3 PE formed a localized mass which was elevated above an adjacent mucosal or serosal surface, or formed an intralumenal projection within a cyst cavity. The sites included ovary (n = 5), pelvic peritoneum and vagina (both n = 3), fallopian tube (n = 2) and colon and appendix (both n = 1). The PE cases were subdivided histologically into two groups. First were those cases that otherwise resembled conventional endometriosis (designated group 1). In these cases the glands were often mildly irregular in shape but tended to be relatively uniform in calibre, and the lining epithelium showed mainly inactive or proliferative endometrioid appearances. In most cases the stromal component resembled that of basal or proliferative endometrium and there was minimal intervening matrix (other than areas with secondary inflammatory or haemorrhagic changes). However, two cases involving the appendix and fallopian tube occurred in pregnant patients and the stromal cells demonstrated decidual-type appearances. Glandular polarity was sometimes © 2015 John Wiley & Sons Ltd, Histopathology, 68, 398–404.
STATISTICS
Summary statistics including means, standard deviations and minimums and maximums were provided for each of the continuous variables. A one-way analysis of variance (ANOVA) was used to compare the groups for age, and for stromal and epithelial p16 expression. Pairwise comparisons were provided for all analyses. All tests were two-sided, with statistical significance set at 5%. Data were analysed using the 8 R environment for statistical computing.
Results Table 1 provides summary statistics for patient age and for stromal and epithelial p16 expression for each group, and Table 2 provides pairwise comparison for all groups. NON-POLYPOID ENDOMETRIOSIS
The mean age was 40.1 years. Corresponding endometrial histology was available in 11 patients showing normal appearances in five cases, endometrial polyp in
400
C J R Stewart & C Bharat
Table 1. Patient age and p16 expression in non-polypoid and polypoid endometriosis groups
Age (years)
Stromal p16 expression (%)
Group
n
NPE
20 40.1
11.3 23
66
Group 1 PE 10 43.4
10.1 29
58
Group 2 PE
12.0 42
74
20 33.8
25.4
0
80
Group 1 PE 10 40.0
29.8
0
80
7.1 60
80
NPE
Group 2 PE
Mean SD
5 59.0
5 70.0
20 13.3 Epithelial p16 NPE expression Group 1 PE 10 20.0 (%) Group 2 PE
5 58.0
Min Max
14.5
0
50
24.9
0
80
36.3 10
90
glands and cyst cavities, whereas endometriotic deposits within fibromuscular stroma and subperitoneal tissues showed more localized p16 expression. By labelling stromal cells, the immunostained slides sometimes highlighted subtle foci of endometriosis (Figure 1). In some cases, reactive myofibroblasts, smooth muscle cells and endothelial cells at the junction between the native stroma and the endometriotic tissue were p16-positive. The endometriotic epithelium also showed p16 expression in 12 specimens (60%), but staining was typically focal, involving single cells or small strips of cells within otherwise unstained glands (mosaic pattern); however, occasionally entire glands were p16-positive. POLYPOID ENDOMETRIOSIS
PE, Polypoid endometriosis; NPE, Non-polypoid endometriosis; SD, Standard deviation; Min, Minimum; Max: Maximum.
three cases (one of which also demonstrated atypical endometrial hyperplasia), grade 1 endometrioid adenocarcinoma in two cases and a disordered proliferative pattern in one case. Immunohistochemistry for CD10 labelled the endometrioid stromal cells in all cases, usually with close to 100% of cells being positive. Stromal p16 staining (≥10% of cells positive) was identified in 17 of 20 cases (85%), with a mean of 33.8% positive cells (range 0–80%, Table 1). The proportion of p16positive stromal cells varied between different endometriotic foci in individual cases, but generally there was more consistent staining around dilated
Group 1 Ten cases resembled NPE histologically, and these involved the vagina (n = 3), ovary and fallopian tube (both n = 2) and the pelvic peritoneum, colon and appendix (all n = 1). The ovarian cases comprised intralumenal nodules within endometriotic cysts, while the peritoneal lesion involved the uterine serosal surface. The vaginal, tubal, colonic and appendiceal lesions all involved mucosal surfaces and formed discrete polypoid nodules that projected into the adjacent lumenal spaces; all three vaginal lesions were submitted clinically as ‘polyps’ (Figure 2). The mean age was 43.4 years. Four patients had endometrial sampling, showing normal appearances in two cases, endometrial polyp in one case and non-necrotizing granulomas of uncertain aetiology in one case. All cases showed CD10 expression in the
Table 2. Pairwise comparisons between non-polypoid and polypoid endometriosis groups
Age (years)
Stromal p16 expression (%)
Epithelial p16 expression (%)
95% CI
P-value
Comparison
Mean difference
Group 2 PE versus Group 1 PE
15.6
3.26–27.94
0.015
Group 2 PE versus NPE
18.9
7.64–30.16
0.002
Group 1 PE versus NPE
3.3
5.42–12.02
0.447
Group 2 PE versus Group 1 PE
30.0
1.87–58.13
0.039
Group 2 PE versus NPE
36.3
10.57–61.93
0.007
Group 1PE versus NPE
6.3
13.64 to 26.14
0.517
Group 2 PE versus Group 1 PE
38.0
13.93–62.07
0.002
Group 2 PE versus NPE
44.8
22.78–66.72
50 years).3 There were similar findings in the present series, and patients with PE resembling endometrial polyps (group 2) were significantly older than patients with either conventional endometriosis-like PE (group 1) or NPE. These age differences could partly explain the previously documented associations of PE with hormonal therapy, including tamoxifen treatment.3,4,9–15 It is worth noting that PE can mimic a malignant neoplasm clinically and radiologically,4,16–21 and that it may be multifocal in distribution.3,4,10,18,22 Occasional cases have also been misinterpreted as histologically malignant.13,23
The present study shows that two histological subtypes of PE can be distinguished. First, there are cases which otherwise resemble NPE histologically, but which involve mucosal or serosal surfaces, or cystic cavities, in which polypoid growth can occur readily. Such cases accounted for 10 of 15 PE cases in this series, and these showed a similar age distribution and p16 expression profile to NPE. These findings suggest that group 1 PE and NPE are fundamentally similar, with polyp formation in the former cases being dependent mainly upon local anatomical factors. The second subgroup of PE cases showed a closer histological resemblance to polyps arising in the endometrium, and thus were more consistent with PE, as described initially by Mostoufizadeh and © 2015 John Wiley & Sons Ltd, Histopathology, 68, 398–404.
Polypoid endometriosis
Scully.4 This morphological similarity has also been noted in subsequent reports.3,10,12,14,23 Thick-walled blood vessels, a characteristic feature of eutopic endometrial polyps, have also been described in PE, although this was not a particular feature of the cases examined herein. Interestingly, three of the four group 2 PE patients with endometrial sampling in the present study had concurrent endometrial polyps, an association that has been noted in previous studies of PE.3,4,10,12,13,15 This raises the possibility of a ‘field effect’ predisposition towards polyp formation in eutopic and ectopic endometrial sites. In this regard, it is worth noting that while endometrial polyps have been considered traditionally to be non-neoplastic lesions, cytogenetic studies suggest that they arise as a result of a monoclonal stromal cell proliferation.24 Interestingly, HMGA1 or HMGA2 gene rearrangements have also been demonstrated in PE and in ‘mass forming endometriosis’ but not in ovarian endometriomas,23,25 suggesting different pathogenetic mechanisms in these subtypes of endometriosis. We also investigated p16 immunoreactivity in our cases, as recent studies have demonstrated that the stromal cells in endometrial polyps often express this protein, whereas normal endometrial stromal cells are negative or show only focal positivity.5,6 Similarly, endometrial polyp-like lesions developing within the myometrium show stromal p16 staining.26 We found that group 2 PE with endometrial polyp-like features demonstrated significantly greater stromal p16 staining than group 1 PE or NPE cases, further supporting the hypothesis that eutopic and endometriotic polyps have a common pathogenetic basis. However, all endometriotic lesions showed greater stromal p16 staining than seen typically in normal endometrium,6 and in the group 1 PE cases this was most marked in the two specimens showing decidual-type change in pregnancy. Decidualization has been noted previously in occasional cases of PE,3 and there is one report of stromal decidualization causing a mucosal mass-like lesion in the colon.27 We are not aware of additional studies examining p16 expression in eutopic or endometriotic decidua, but staining of a small series of miscarriage specimens showed staining in a minority of cells (mean 10%). Thus decidualized stromal cells in endometriosis, like endometriotic stromal cells generally, appear to show up-regulation of p16 expression. We also found that group 2 PE showed more epithelial p16 expression than the other endometriosis subgroups. The mechanism of p16 up-regulation in polypoid stromal and epithelial cells is uncertain, although the physiological role of p16 protein as an inhibitory cell cycle regulator is well established. In © 2015 John Wiley & Sons Ltd, Histopathology, 68, 398–404.
403
the neoplastic context, p16 dysregulation can occur through a variety of mechanisms,28 but increased p16 expression could also reflect a senescence-type cellular process,29,30 as has been suggested to occur in endometrial polyps.5 Epithelial staining in such cases could also reflect the higher incidence of epithelial metaplasia in polypoid lesions, as it is well-recognized that metaplastic changes in the endometrium can be associated with increased p16 expression.31–33 In summary, PE appears to include two processes. In the majority of cases PE otherwise resembles conventional endometriosis, but involvement of mucosal or subserosal sites, or the lining of cyst cavities, permits polypoid growth. Less commonly, PE resembles eutopic endometrial polyps, and these lesions usually occur in older individuals and demonstrate significantly increased stromal and epithelial p16 expression supporting a common pathogenesis. However, endometriotic stromal cells also showed increased p16 expression compared to normal endometrium. The mechanism of p16 up-regulation in endometriotic tissue is uncertain, but this could reflect the activation of cellular senescence pathways.
References 1. Giudice LC. Endometriosis. N. Engl. J. Med. 2010; 362; 8. 2. Clement PB. The pathology of endometriosis. A survey of the many faces of a common disease emphasizing diagnostic pitfalls and unusual and newly appreciated aspects. Adv. Anat. Pathol. 2007; 14; 241–260. 3. Parker RL, Dadmanesh F, Young RH, Clement PB. Polypoid endometriosis. A clinicopathologic analysis of 24 cases and a review of the literature. Am. J. Surg. Pathol. 2004; 28; 285–297. 4. Mostoufizadeh M, Scully RE. Malignant tumors arising in endometriosis. Clin. Obstet. Gynecol. 1980; 23; 951–963. 5. Moritani S, Ichihara S, Hasegawa M et al. Stromal p16 expression differentiates endometrial polyp from endometrial hyperplasia. Virchows Arch. 2012; 461; 141–148. 6. Stewart CJR, Bharat C, Crook M. p16 immunoreactivity in endometrial stromal cells: stromal p16 expression characterises but is not specific for endometrial polyps. Pathology 2015; 47; 112–117. 7. Stewart CJR, Leake R. Endometrial synovial-like metaplasia associated with levonorgestrel-releasing intrauterine system. Int. J. Gynecol. Pathol. in press. 8. R Development Core Team. R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing, 2015: ISBN 3-900051-07-0. Available at: http://www.R-project.org/. 9. Chang CK, Chen P, Leu FJ, Lou SM. Florid polypoid endometriosis exacerbated by tamoxifen therapy in breast cancer. Obstet. Gynecol. 2003; 102; 1127–1130. 10. Schlesinger C, Silverberg SG. Tamoxifen-associated polyps (basalomas) arising in multiple endometriotic foci: a case report and review of the literature. Gynecol. Oncol. 1999; 73; 305–311. 11. Kraft JK, Hughes T. Polypoid endometriosis and other benign gynaecological complications associated with tamoxifen
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therapy – a case to illustrate features on magnetic resonance imaging. Clin. Radiol. 2006; 61; 198–201. Ismail SM, Maulik TG. Tamoxifen-associated post-menopausal endometriosis. Histopathology 1997; 30; 1. Felix A, Nogales FF, Arias-Stella J. Polypoid endometriosis of the uterine cervix with Arias-Stella reaction in a patient taking phytoestrogens. Int. J. Gynecol. Pathol. 2010; 29; 185–188. Othman NH, Othman MS, Ismail AN et al. Multiple polypoid endometriosis: a rare complication following withdrawal of gonadotropin releasing hormone (GnRH) agonist for severe endometriosis: a case report. Aust. NZ J. Obstet. Gynaecol. 1996; 362; 216–218. Chang A, Nataragan S. Polypoid endometriosis. Arch. Pathol. Lab. Med. 2001; 125; 1257. Dadhwal V, Deka D, Mathur S et al. Vaginal polypoid endometriosis simulating neoplasia in a young woman. J. Low Genit. Tract. Dis. 2012; 16; 318–321. Jaiman S, Gundabattula SR, Pochiraju M, Sangireddy JR. Polypoid endometriosis of the cervix: a case report and review of the literature. Arch. Gynecol. Obstet. 2014; 289; 915–920. Kaushal S, Dadhwal V, Mathur SR et al. Multifocal polypoid endometriosis in a young woman simulating vaginal and pelvic neoplasm. J. Clin. Pathol. 2010; 63; 452–454. Lambrechts S, van Calsteren K, Capoen A et al. Polypoid endometriosis of the bladder during pregnancy mimicking urachal carcinoma. Ultrasound Obstet. Gynaecol. 2011; 38; 475–478. Yantiss RK, Clement PB, Young RH. Endometriosis of the intestinal tract: a study of 44 cases of a disease that may cause diverse challenges in clinical and pathologic evaluation. Am. J. Surg. Pathol. 2001; 25; 445–454. Jiang W, Roma AA, Lai K, Carver P, Xiao SY, Liu X. Endometriosis involving the mucosa of the intestinal tract: a clinicopathologic study of 15 cases. Mod. Pathol. 2013; 26; 1270–1278. Laird LA, Hoffman JS, Omrani A. Multifocal polypoid endometriosis presenting as huge pelvic masses causing
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deep vein thrombosis. Arch. Pathol. Lab. Med. 2004; 128; 561– 564. Medeiros F, Wang X, Araujo ARC et al. HMGA gene rearrangement is a recurrent somatic alteration in polypoid endometriosis. Hum. Pathol. 2012; 43; 1243–1248. Crum CP, Hornstein MD, Stewart EA. Evaluation of cyclic endometrium and benign endometrial disorders. In Crum CP, Lee KR eds. Diagnostic gynecologic and obstetric pathology. Philadelphia: Elsevier Saunders, 2006; 441–491. Medeiros F, Araujo AR, Erickson-Johnson MR et al. HMGA1 and HMGA2 rearrangements in mass-forming endometriosis. Genes Chromosomes Cancer 2010; 49; 630–634. Stewart CJR. Endometrial polyp-like lesions arising in adenomyosis: a report of 3 cases. Pathology. 2015; 47; 478–479. Park HS, Jang KY, Moon WS. Predecidualized endometriosis presenting as rectosigmoid polyps with stenosis. J. Gastrointestin. Liver Dis. 2012; 21; 7. Sherr CJ. The INK4a/ARF network in tumour suppression. Nat. Rev. Mol. Cell Biol. 2001; 2; 731–737. Witkiewicz AK, Knudsen KE, Dicker AP, Knudsen ES. The meaning of p16ink4a expression in tumors. Functional significance, clinical associations and future developments. Cell Cycle 2011; 10; 2497–2503. LaPak KM, Burd CE. The molecular balancing act of p16INK4a in cancer and aging. Mol. Cancer Res. 2014; 12; 167–183. Nicolae A, Preda O, Aneiros-Fernandez J et al. p16INK4A positivity identifies endometrial surface papillary syncytial change as a regressive feature associated with desquamation. Histopathology 2011; 58; 483–486. McCluggage WG, McBride HA. Papillary syncytial metaplasia associated with endometrial breakdown exhibits an immunophenotype that overlaps with uterine serous carcinoma. Int. J. Gynecol. Pathol. 2012; 31; 206–210. Nicolae A, Preda O, Nogales FF. Endometrial metaplasias and reactive changes: a spectrum of altered differentiation. J. Clin. Pathol. 2011; 64; 97–106.
© 2015 John Wiley & Sons Ltd, Histopathology, 68, 398–404.
Clinicopathological and immunohistological features of polypoid endometriosis Colin JR Stewart1,2 & Chrianna Bharat3,4 1
Department of Pathology, King Edward Memorial Hospital, 2School of Women’s and Infants’ Health, 3Centre for Applied Statistics, University of Western Australia, and 4Department of Research, Sir Charles Gairdner Hospital, Perth, WA, Australia
Date of submission 5 May 2015 Accepted for publication 5 June 2015 Published online Article Accepted 10 June 2015
Stewart C JR & Bharat C (2016) Histopathology 68, 398–404. DOI: 10.1111/his.12755
Clinicopathological and immunohistological features of polypoid endometriosis Aims: To compare clinicopathological and immunohistochemical features of polypoid endometriosis (PE) and non-polypoid endometriosis (NPE). Methods and results: Fifteen cases of PE and 20 cases of NPE were assessed. All cases were stained immunohistochemically for CD10 and p16 and the proportion of p16-positive stromal and epithelial cells was estimated. On review, 10 PE cases resembled NPE histologically but occurred at mucosal or serosal surfaces, or within cyst cavities, that permitted polyp formation. These cases had a similar age distribution and immunohistochemical profile to NPE. The remaining five PE cases showed histological similarity
to eutopic endometrial polyps; these occurred in older patients, and showed significantly greater stromal and epithelial p16 immunoreactivity. Conclusions: There are two main subgroups of PE. The majority of cases in this series showed similar histological features to NPE, but involved anatomical sites that facilitated exophytic or polypoid growth. The remaining PE cases resembled eutopic endometrial polyps histologically and immunophenotypically and they occurred in older patients. These findings suggest that such lesions are ‘true’ polyps sharing a pathogenetic relationship with similar lesions arising in the endometrium.
Keywords: endometrial polyp, endometriosis, immunohistochemistry, polypoid, p16
Introduction Endometriosis, defined as the presence of endometriotic glandular and stromal tissue outside the uterine corpus, is one of the most common gynaecological pathological processes, being identified in 10–15% of all women.1 While the diagnosis of endometriosis is usually straightforward, pathologists need to be aware of the many histological variants of this common condition, some of which can present diagnostic difficulty.2 One interesting variant is so-called polypoid endometriosis (PE), which has been the subject of only one detailed study.3 To the best of our
Address for correspondence: C JR Stewart, Department of Histopathology, King Edward Memorial Hospital, Bagot Road, Perth, WA 6008, Australia. e-mail: [email protected] © 2015 John Wiley & Sons Ltd.
knowledge, the term PE (or ‘endometriotic polyposis’) was introduced by Mostoufizadeh and Scully for cases of endometriosis which resembled an endometrial polyp microscopically.4 In their series, Parker et al. broadened the term to include cases of endometriosis that were simply polypoid from the gross aspect.3 In this study we present a series of 15 cases of cases of PE, including cases that fit the original stricter definition of Mostoufizadeh and Scully,4 but additionally cases that met the broader criteria of Parker et al.4 to investigate further the differing clinical and microscopic aspects of these two forms of endometriosis. Because recent studies have suggested that stromal cell p16 expression is characteristic of (eutopic) endometrial polyps,5,6 we also compared CD10 and p16 immunoreactivity in these lesions, and in a series of conventional (non-polypoid) endometriotic lesions.
Polypoid endometriosis
399
The specimens were obtained from the histopathology files of King Edward Memorial Hospital, Perth. All samples were fixed in buffered formalin and processed routinely to paraffin wax. Serial 4-l sections were stained with haematoxylin and eosin (H&E) and immunohistochemically, as described below. Two main groups of cases were investigated, conventional or non-polypoid endometriosis (NPE) and PE. Patient age and the histological appearances of the endometrium, when available, were recorded. Details of hormonal therapy were not available in these cases. The study received institutional ethics approval (KEMH reference 8567).
present, to some extent mimicking normal endometrium. Second were those cases where the glandular and stromal appearances resembled more closely those seen in eutopic endometrial polyps (designated group 2). In these cases the glands typically exhibited a range in calibre, often with focal cystic change, and the lining epithelium frequently demonstrated metaplastic alterations (mucinous, ciliated and/or eosinophilic). The stroma included plump, ovoid- to spindle-shaped cells which were separated by a relatively abundant, mature collagenous matrix. Thickwalled blood vessels, characteristic of eutopic endometrial polyps, were not a prominent feature of either type of PE in this series.
NON-POLYPOID ENDOMETRIOSIS
IMMUNOHISTOCHEMISTRY
Twenty-two biopsy or resection specimens from 20 patients were examined. These were selected randomly from cases encountered over a 2-year period to demonstrate endometriosis occurring in a variety of anatomical sites. The sites comprised pelvic peritoneum including the uterine serosa (n = 5), ovary (n = 4), colorectum and vagina (both n = 3), appendix, fallopian tube and ureter (all n = 2) and pelvic lymph node (n = 1).
Immunohistochemistry for p16 protein and CD10 was performed as described previously.6,7 Immunostaining for p16 was assessed separately within the epithelial and stromal components, and the percentage of positive cells was estimated to the closest 10%.6 As staining intensity was strong in all positive cases, this was not recorded separately. For the two NPE cases with two samples the average staining percentage was used in the analysis.
Materials and methods
POLYPOID ENDOMETRIOSIS
Fifteen consecutive cases of PE identified by one author (C.J.R.S.) during a 5-year period were studied. As defined previously,3 PE formed a localized mass which was elevated above an adjacent mucosal or serosal surface, or formed an intralumenal projection within a cyst cavity. The sites included ovary (n = 5), pelvic peritoneum and vagina (both n = 3), fallopian tube (n = 2) and colon and appendix (both n = 1). The PE cases were subdivided histologically into two groups. First were those cases that otherwise resembled conventional endometriosis (designated group 1). In these cases the glands were often mildly irregular in shape but tended to be relatively uniform in calibre, and the lining epithelium showed mainly inactive or proliferative endometrioid appearances. In most cases the stromal component resembled that of basal or proliferative endometrium and there was minimal intervening matrix (other than areas with secondary inflammatory or haemorrhagic changes). However, two cases involving the appendix and fallopian tube occurred in pregnant patients and the stromal cells demonstrated decidual-type appearances. Glandular polarity was sometimes © 2015 John Wiley & Sons Ltd, Histopathology, 68, 398–404.
STATISTICS
Summary statistics including means, standard deviations and minimums and maximums were provided for each of the continuous variables. A one-way analysis of variance (ANOVA) was used to compare the groups for age, and for stromal and epithelial p16 expression. Pairwise comparisons were provided for all analyses. All tests were two-sided, with statistical significance set at 5%. Data were analysed using the 8 R environment for statistical computing.
Results Table 1 provides summary statistics for patient age and for stromal and epithelial p16 expression for each group, and Table 2 provides pairwise comparison for all groups. NON-POLYPOID ENDOMETRIOSIS
The mean age was 40.1 years. Corresponding endometrial histology was available in 11 patients showing normal appearances in five cases, endometrial polyp in
400
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Table 1. Patient age and p16 expression in non-polypoid and polypoid endometriosis groups
Age (years)
Stromal p16 expression (%)
Group
n
NPE
20 40.1
11.3 23
66
Group 1 PE 10 43.4
10.1 29
58
Group 2 PE
12.0 42
74
20 33.8
25.4
0
80
Group 1 PE 10 40.0
29.8
0
80
7.1 60
80
NPE
Group 2 PE
Mean SD
5 59.0
5 70.0
20 13.3 Epithelial p16 NPE expression Group 1 PE 10 20.0 (%) Group 2 PE
5 58.0
Min Max
14.5
0
50
24.9
0
80
36.3 10
90
glands and cyst cavities, whereas endometriotic deposits within fibromuscular stroma and subperitoneal tissues showed more localized p16 expression. By labelling stromal cells, the immunostained slides sometimes highlighted subtle foci of endometriosis (Figure 1). In some cases, reactive myofibroblasts, smooth muscle cells and endothelial cells at the junction between the native stroma and the endometriotic tissue were p16-positive. The endometriotic epithelium also showed p16 expression in 12 specimens (60%), but staining was typically focal, involving single cells or small strips of cells within otherwise unstained glands (mosaic pattern); however, occasionally entire glands were p16-positive. POLYPOID ENDOMETRIOSIS
PE, Polypoid endometriosis; NPE, Non-polypoid endometriosis; SD, Standard deviation; Min, Minimum; Max: Maximum.
three cases (one of which also demonstrated atypical endometrial hyperplasia), grade 1 endometrioid adenocarcinoma in two cases and a disordered proliferative pattern in one case. Immunohistochemistry for CD10 labelled the endometrioid stromal cells in all cases, usually with close to 100% of cells being positive. Stromal p16 staining (≥10% of cells positive) was identified in 17 of 20 cases (85%), with a mean of 33.8% positive cells (range 0–80%, Table 1). The proportion of p16positive stromal cells varied between different endometriotic foci in individual cases, but generally there was more consistent staining around dilated
Group 1 Ten cases resembled NPE histologically, and these involved the vagina (n = 3), ovary and fallopian tube (both n = 2) and the pelvic peritoneum, colon and appendix (all n = 1). The ovarian cases comprised intralumenal nodules within endometriotic cysts, while the peritoneal lesion involved the uterine serosal surface. The vaginal, tubal, colonic and appendiceal lesions all involved mucosal surfaces and formed discrete polypoid nodules that projected into the adjacent lumenal spaces; all three vaginal lesions were submitted clinically as ‘polyps’ (Figure 2). The mean age was 43.4 years. Four patients had endometrial sampling, showing normal appearances in two cases, endometrial polyp in one case and non-necrotizing granulomas of uncertain aetiology in one case. All cases showed CD10 expression in the
Table 2. Pairwise comparisons between non-polypoid and polypoid endometriosis groups
Age (years)
Stromal p16 expression (%)
Epithelial p16 expression (%)
95% CI
P-value
Comparison
Mean difference
Group 2 PE versus Group 1 PE
15.6
3.26–27.94
0.015
Group 2 PE versus NPE
18.9
7.64–30.16
0.002
Group 1 PE versus NPE
3.3
5.42–12.02
0.447
Group 2 PE versus Group 1 PE
30.0
1.87–58.13
0.039
Group 2 PE versus NPE
36.3
10.57–61.93
0.007
Group 1PE versus NPE
6.3
13.64 to 26.14
0.517
Group 2 PE versus Group 1 PE
38.0
13.93–62.07
0.002
Group 2 PE versus NPE
44.8
22.78–66.72
50 years).3 There were similar findings in the present series, and patients with PE resembling endometrial polyps (group 2) were significantly older than patients with either conventional endometriosis-like PE (group 1) or NPE. These age differences could partly explain the previously documented associations of PE with hormonal therapy, including tamoxifen treatment.3,4,9–15 It is worth noting that PE can mimic a malignant neoplasm clinically and radiologically,4,16–21 and that it may be multifocal in distribution.3,4,10,18,22 Occasional cases have also been misinterpreted as histologically malignant.13,23
The present study shows that two histological subtypes of PE can be distinguished. First, there are cases which otherwise resemble NPE histologically, but which involve mucosal or serosal surfaces, or cystic cavities, in which polypoid growth can occur readily. Such cases accounted for 10 of 15 PE cases in this series, and these showed a similar age distribution and p16 expression profile to NPE. These findings suggest that group 1 PE and NPE are fundamentally similar, with polyp formation in the former cases being dependent mainly upon local anatomical factors. The second subgroup of PE cases showed a closer histological resemblance to polyps arising in the endometrium, and thus were more consistent with PE, as described initially by Mostoufizadeh and © 2015 John Wiley & Sons Ltd, Histopathology, 68, 398–404.
Polypoid endometriosis
Scully.4 This morphological similarity has also been noted in subsequent reports.3,10,12,14,23 Thick-walled blood vessels, a characteristic feature of eutopic endometrial polyps, have also been described in PE, although this was not a particular feature of the cases examined herein. Interestingly, three of the four group 2 PE patients with endometrial sampling in the present study had concurrent endometrial polyps, an association that has been noted in previous studies of PE.3,4,10,12,13,15 This raises the possibility of a ‘field effect’ predisposition towards polyp formation in eutopic and ectopic endometrial sites. In this regard, it is worth noting that while endometrial polyps have been considered traditionally to be non-neoplastic lesions, cytogenetic studies suggest that they arise as a result of a monoclonal stromal cell proliferation.24 Interestingly, HMGA1 or HMGA2 gene rearrangements have also been demonstrated in PE and in ‘mass forming endometriosis’ but not in ovarian endometriomas,23,25 suggesting different pathogenetic mechanisms in these subtypes of endometriosis. We also investigated p16 immunoreactivity in our cases, as recent studies have demonstrated that the stromal cells in endometrial polyps often express this protein, whereas normal endometrial stromal cells are negative or show only focal positivity.5,6 Similarly, endometrial polyp-like lesions developing within the myometrium show stromal p16 staining.26 We found that group 2 PE with endometrial polyp-like features demonstrated significantly greater stromal p16 staining than group 1 PE or NPE cases, further supporting the hypothesis that eutopic and endometriotic polyps have a common pathogenetic basis. However, all endometriotic lesions showed greater stromal p16 staining than seen typically in normal endometrium,6 and in the group 1 PE cases this was most marked in the two specimens showing decidual-type change in pregnancy. Decidualization has been noted previously in occasional cases of PE,3 and there is one report of stromal decidualization causing a mucosal mass-like lesion in the colon.27 We are not aware of additional studies examining p16 expression in eutopic or endometriotic decidua, but staining of a small series of miscarriage specimens showed staining in a minority of cells (mean 10%). Thus decidualized stromal cells in endometriosis, like endometriotic stromal cells generally, appear to show up-regulation of p16 expression. We also found that group 2 PE showed more epithelial p16 expression than the other endometriosis subgroups. The mechanism of p16 up-regulation in polypoid stromal and epithelial cells is uncertain, although the physiological role of p16 protein as an inhibitory cell cycle regulator is well established. In © 2015 John Wiley & Sons Ltd, Histopathology, 68, 398–404.
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the neoplastic context, p16 dysregulation can occur through a variety of mechanisms,28 but increased p16 expression could also reflect a senescence-type cellular process,29,30 as has been suggested to occur in endometrial polyps.5 Epithelial staining in such cases could also reflect the higher incidence of epithelial metaplasia in polypoid lesions, as it is well-recognized that metaplastic changes in the endometrium can be associated with increased p16 expression.31–33 In summary, PE appears to include two processes. In the majority of cases PE otherwise resembles conventional endometriosis, but involvement of mucosal or subserosal sites, or the lining of cyst cavities, permits polypoid growth. Less commonly, PE resembles eutopic endometrial polyps, and these lesions usually occur in older individuals and demonstrate significantly increased stromal and epithelial p16 expression supporting a common pathogenesis. However, endometriotic stromal cells also showed increased p16 expression compared to normal endometrium. The mechanism of p16 up-regulation in endometriotic tissue is uncertain, but this could reflect the activation of cellular senescence pathways.
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