Human Pathology (2015) 46, 1204–1208
www.elsevier.com/locate/humpath
Original contribution
A subset of prostatic basal cell carcinomas harbor the MYB rearrangement of adenoid cystic carcinoma☆,☆☆ Justin A. Bishop MD a,b,⁎, Raluca Yonescu MD a , Jonathan I. Epstein MD a,c,d , William H. Westra MD a,b,c a
Department of Pathology, The Johns Hopkins Medical Institutions, Baltimore, MD 21231 Department of Otolaryngology/Head and Neck Surgery, The Johns Hopkins Medical Institutions, Baltimore, MD 21231 c Department of Urology, The Johns Hopkins Medical Institutions, Baltimore, MD 21231 d Department of Oncology, The Johns Hopkins Medical Institutions, Baltimore, MD 21231 b
Received 10 February 2015; revised 1 May 2015; accepted 7 May 2015
Keywords: Prostate; Adenoid cystic carcinoma; Basal cell carcinoma; MYB-NFIB; Fluorescence in situ hybridization
Summary Adenoid cystic carcinoma (ACC) is a basaloid tumor consisting of myoepithelial and ductal cells typically arranged in a cribriform pattern. Adenoid cystic carcinoma is generally regarded as a form of salivary gland carcinoma, but it can arise from sites unassociated with salivary tissue. A rare form of prostate carcinoma exhibits ACC-like features; it is no longer regarded as a true ACC but rather as prostatic basal cell carcinoma (PBCC) and within the spectrum of basaloid prostatic proliferations. True ACCs often harbor MYB translocations resulting in the MYB-NFIB fusion protein. MYB analysis could clarify the true nature of prostatic carcinomas that exhibit ACC features and thus help refine the classification of prostatic basaloid proliferations. Twelve PBCCs were identified from the pathology consultation files of Johns Hopkins Hospital. The histopathologic features were reviewed, and breakapart fluorescence in situ hybridization for MYB was performed. All 12 cases exhibited prominent basaloid histology. Four were purely solid, 7 exhibited a cribriform pattern reminiscent of salivary ACC, and 1 had a mixed pattern. The MYB rearrangement was detected in 2 (29%) of 7 ACC-like carcinomas but in none (0%) of the 5 PBCCs with a prominent solid pattern. True ACCs can arise in the prostate as is evidenced by the presence of the characteristic MYB rearrangement. When dealing with malignant basaloid proliferations in the prostate, recommendations to consolidate ACCs with other tumor types may need to be reassessed, particularly in light of the rapidly advancing field of biologic therapy where the identification of tumor-specific genetic alterations presents novel therapeutic targets. © 2015 Elsevier Inc. All rights reserved.
1. Introduction ☆
Competing interests: The authors have no conflicts of interest to declare. Funding/Support: This study was funded in part by the National Institutes of Health/National Institute of Dental and Craniofacial Research (NIH/NIDCR) Head and Neck SPORE Grant P50 DE019032. ⁎ Corresponding author at: The Johns Hopkins University School of Medicine, 401 N. Broadway, Weinberg 2249, Baltimore, MD 21231. E-mail address: [email protected] (J. A. Bishop). ☆☆
http://dx.doi.org/10.1016/j.humpath.2015.05.002 0046-8177/© 2015 Elsevier Inc. All rights reserved.
Adenoid cystic carcinoma (ACC) is a salivary gland tumor that is composed of ductal and myoepithelial cells. Adenoid cystic carcinoma can also arise in sites unassociated with salivary gland tissue including the skin, cervix, and breast [1-5]. The existence of a prostatic form of ACC is controversial. At one time recognized by the World Health
MYB rearrangements in prostatic basal cell carcinomas Organization (WHO) classification of prostatic tumors as a true tumor entity [6], prostatic ACC has since been discarded as a diagnostic category in more recent WHO classification schemes [7]. This reconsideration was prompted by 2 observations. First, myoepithelial cells are not indigenous to the prostate such that a myoepithelial form of prostatic carcinoma is entirely unanticipated at this site. Second, the adenoid cystic morphology occurs along a spectrum of basaloid proliferations that encompasses basal cell hyperplasia, basal cell adenoma, and basal cell basal cell carcinoma [8-12]. Accordingly, current WHO classification has combined ACC with other malignant basaloid tumors of the prostate under the single term basal cell carcinoma, at least until studies can establish a more compelling link to true ACC than mere phenotypic similarities [7]. Recent studies have shown that ACCs often harbor a recurrent t(6;9)(q22-23;p23-24) translocation resulting in a novel fusion of the MYB proto-oncogene with the NFIB transcription factor gene [13,14]. The fusion is not detected in non-ACCs, but its consistent presence in ACCs across various anatomical sites including salivary gland, sinonasal cavity, tracheobronchial tree, larynx, breast, and vulva clearly links the adenoid cystic phenotype with a specific molecular pathway [1,14,15]. Toward that end, we evaluated prostatic basal cell carcinoma (PBCCs) for the presence of the MYB-NFIB translocation to determine if this defining genetic alteration could help refine the classification of this controversial group of tumors.
2. Materials and methods This study was approved by The Johns Hopkins Institutional Review Board (IRB05070101). Histologic slides and paraffin-embedded tissue blocks from 12 PBCCs were retrieved from the surgical pathology consultation files of 1 of the authors (J.I.E.). Fluorescence in situ hybridization was performed on formalin-fixed, paraffin-embedded sections using a commercially available MYB dual-color break-apart probe (ZTV-Z-2143-200, ZytoVision, Bremerhaven, Germany). The probe was designed to detect translocations involving the chromosomal region 6q23.3 harboring the MYB gene. Before hybridization, the slides were deparaffinized using a VP 2000 processor (Abbott Molecular, Des Plains, IL). The slides and the MYB probe were codenatured at 80°C for 7 minutes and allowed to anneal over night at 37°C in humidified atmosphere. At the end of the incubation, the slides were washed in 2× SSC/ 0.3% NP-40 for 2 minutes at 72°C and for 2 minutes at room temperature in 2× SSC. The slides were counterstained with DAPI, and a cover slip was applied using Vectashield mounting medium (H-1000, Vector Laboratories, Inc., Burlingame, CA). A fluorescence microscope was used to evaluate the probe pattern. Cells with 2 fusion signals of 1 orange and 1 green fluorochrome were scored as normal and considered negative for MYB break apart (MYB negative). A signal pattern consisting of 1 fusion signal and 1 orange and 1 green signal
1205 at distance from each other indicated 1 normal 6q23.3 locus and 1 locus affected by a translocation.
3. Results All cases were transurethral resections of the prostate. The patients ranged in age from 65 to 86 years (mean, 72 years). Notably, none of the patients had a known history of prior head and neck carcinoma. The morphological features of the tumors are summarized in the Table. Each tumor exhibited overtly infiltrative growth and shared prominent basaloid morphology, but there existed a spectrum of histologic changes. Four tumors (25%) exhibited tumor necrosis, and 2 (17%) demonstrated perineural invasion. Seven cases (54%) (cases 1-7) exhibited morphological findings highly reminiscent of ACC (Fig. 1A), whereas 4 cases (33%) (cases 9-12) consisted purely of solid nests of basaloid cells and did not resemble ACC closely (Fig. 1B). The ACC-like tumors demonstrated a biphasic pattern consisting of varying proportions of basaloid cribriform structures and nests admixed with centrally located tubules with eosinophilic cytoplasm (Fig. 1A, C, D). The eosinophilic tubules were generally abundant, but in 2 cases (cases 4 and 5), they were relatively focal and indistinct. One of these ACC-like cases (case 6) also contained pseudocystic spaces filled with basement membrane material (Fig. 1A), and in case 3, the eosinophilic tubules exhibited cytoplasmic vacuolization. In contrast, the solid-patterned carcinomas showed no cribriforming or tubular structures (Fig. 1B). Of these solid-patterned carcinomas, 3 demonstrated areas of comedonecrosis within some of the tumor nests. Finally, 1 tumor (case 8) had a mixed pattern; it grew predominantly as zones of solid nests but also demonstrated focal areas of biphasic growth with nests admixed with eosinophilic tubules (Fig. 1E and F). Overall, 2 (17%) of 12 PBCCs were positive for a MYB rearrangement by fluorescence in situ hybridization (Figs. 2 and 3). The positive cases were restricted to the adenoid cystic-like basal cell carcinomas without solid growth (2/7, 29%) (Fig. 2). One of the MYB-rearranged cases (case 5) exhibited a purely cribriform growth pattern (Fig. 2A), whereas the other case (case 1) had mixed tubular and cribriform features (Fig. 2B). In contrast, the MYB rearrangement was not identified in any of the 5 basal cell carcinomas that were entirely or predominantly solid in pattern. Of the 2 MYB-rearranged cases, 1 exhibited perineural invasion compared with 1 of 10 cases without MYB rearrangements.
4. Discussion Chromosome rearrangements, in particular translocations, may result in fusion oncogenes encoding oncoproteins with transforming properties. Most gene fusions are found in leukemias and sarcomas, but several carcinomas have also
1206
J. A. Bishop et al.
Table
The histopathologic and molecular features of 12 PBCCs
Case
Microscopic features
MYB rearrangement
1 2 3 4 5 6 7 8 9 10 11 12
Basaloid nests and cribriform glands with abundant central eosinophilic tubules Basaloid nests and cribriform glands with abundant central eosinophilic tubules Basaloid nests and cribriform glands with abundant central eosinophilic and vacuolated tubules Basaloid nests and cribriform glands with indistinct eosinophilic tubules Cribriform glands with indistinct eosinophilic tubules Basaloid nests and cribriform glands with abundant central eosinophilic tubules and pseudocystic spaces Basaloid nests and cribriform glands with abundant central eosinophilic tubules Predominantly solid basaloid nests, with areas of nests containing central eosinophilic tubules Solid basaloid nests Solid basaloid nests with necrosis Solid basaloid nests with necrosis Solid basaloid nests with necrosis
+ − − − + − − − − − − −
been shown to express fusion oncogenes. Most notably, the ETS and TMPRRS2 fusions are found in most prostate carcinomas [16]. Several gene fusions have also been identified in salivary
gland neoplasms [17-20]. As one important example, ACCs often harbor a recurrent t(6;9)(q22-23;p23-24) translocation resulting in a fusion of the MYB oncogene to the transcription
Fig. 1 The prostate basal cell carcinomas ranged from tubular and cribriform (A) to purely solid (B) in architecture. Most of the tubular and cribriform carcinomas (C and D) also exhibited numerous central ducts with eosinophilic cytoplasm. One basal cell carcinoma had mixed features, with areas of both tubular (E) and solid (F) growth. (For each, hematoxylin and eosin, original magnification ×40).
MYB rearrangements in prostatic basal cell carcinomas
1207
Fig. 2 The 2 carcinomas that harbored MYB rearrangements had histologic features that were highly reminiscent of adenoid cystic carcinoma of salivary glands. One case showed a predominantly cribriform growth pattern (A), whereas the other case had a mixed tubular and cribriform appearance (B). (For each, hematoxylin and eosin, ×40).
factor gene NFIB [1,13,14]. The MYB-NFIB fusion has not been found in any non-ACC carcinomas, such that its detection may be exploited as a diagnostic biomarker for identifying ACC in the head and neck and other sites. Our results show that a subset of PBCCs harbors rearrangement of MYB. The MYB rearrangement was limited to those PBCCs that closely resembled salivary gland ACC. The presence of a specific genetic link with ACC supports the early but discarded view that a subset of PBCCs does represent a true form of ACC. Although the MYB rearrangement was not present in all of the prostatic carcinomas with an adenoid cystic-like morphology, its incidence (29%) falls within the range reported for ACCs of the head and neck (28%-49%) [1,17,21-23]. Moreover, its absence in purely or predominantly solid basal cell carcinomas casts some doubt on the current classification scheme that views all basaloid carcinomas of the prostate as single tumor type. Prostatic basal cell carcinoma is very rare (n = 29 in the largest series) [12], and it is difficult to make definitive conclusions based on our relatively limited number of cases. If, however, our findings are replicated on additional cases of PBCC, classification schemes of primary prostatic carcinomas may need to be modified to again
recognize ACC as a specific entity that warrants separation from the solid basal cell carcinoma. Once regarded as an indolent tumor based on small case numbers with short follow-up [24,25], larger studies with longer follow-up have disclosed that the behavior of PBCCs with adenoid cystic-like features is quite in keeping with ACC including infiltrative growth, local recurrence, metastatic spread to distant sites, and patient death [8-11]. Although ACCs are notoriously unresponsive to conventional chemotherapy, recognition of an activated genetic pathway now opens the way for directed therapy regardless of tumor origin. In the MYB-NFIB fusion oncogene, the 3′ end of MYB, including target sites for negatively regulating microRNAs, is replaced by 1 or more of the coding exons of NFIB [26]. The predicted MYB-NFIB fusion protein retains the DNA binding and transactivation domains of MYB and can activate various genes regulating cell growth and differentiation including BCL2, KIT, CD34, BIRC3, MYC, and MAD1L1. In effect, more accurate refinement of prostatic basaloid neoplasms is more than just a nosologic triviality but may help tailor treatment based on an association of tumor phenotype with an activated genetic pathway that includes various potential therapeutic targets.
Fig. 3 This tumor (case 1) had an ACC-like appearance (A) (hematoxylin and eosin, ×400) and harbored a MYB rearrangement as indicated by the red and greed signals on this break-apart fluorescent in situ hybridization assay (B).
1208
References [1] Brill II LB, Kanner WA, Fehr A, et al. Analysis of MYB expression and MYB-NFIB gene fusions in adenoid cystic carcinoma and other salivary neoplasms. Mod Pathol 2011;24:1169-76. [2] Woida FM, Ribeiro-Silva A. Adenoid cystic carcinoma of the Bartholin gland: an overview. Arch Pathol Lab Med 2007;131:796-8. [3] Ramakrishnan R, Chaudhry IH, Ramdial P, et al. Primary cutaneous adenoid cystic carcinoma: a clinicopathologic and immunohistochemical study of 27 cases. Am J Surg Pathol 2013;37:1603-11. [4] Bennett AK, Mills SE, Wick MR. Salivary-type neoplasms of the breast and lung. Semin Diagn Pathol 2003;20:279-304. [5] Moran CA, Suster S, Koss MN. Primary adenoid cystic carcinoma of the lung. A clinicopathologic and immunohistochemical study of 16 cases. Cancer 1994;73:1390-7. [6] Mostofi FK, Sesterhenn I, Sobin LH. Histological Typing of Prostate Tumours. Geneva: World Health Organization; 1980. [7] Eble JN, Sauter G, Epstein JI, Sesterhenn IA. World Health Organization Classification of Tumours of the Urinary System and Male Genital Organs. Lyon, France: IARC Press; 2004. [8] Ayyathurai R, Civantos F, Soloway MS, Manoharan M. Basal cell carcinoma of the prostate: current concepts. BJU Int 2007;99:1345-9. [9] McKenney JK, Amin MB, Srigley JR, et al. Basal cell proliferations of the prostate other than usual basal cell hyperplasia: a clinicopathologic study of 23 cases, including four carcinomas, with a proposed classification. Am J Surg Pathol 2004;28:1289-98. [10] Iczkowski KA, Ferguson KL, Grier DD, et al. Adenoid cystic/basal cell carcinoma of the prostate: clinicopathologic findings in 19 cases. Am J Surg Pathol 2003;27:1523-9. [11] Begnami MD, Quezado M, Pinto P, Linehan WM, Merino M. Adenoid cystic/basal cell carcinoma of the prostate: review and update. Arch Pathol Lab Med 2007;131:637-40. [12] Ali TZ, Epstein JI. Basal cell carcinoma of the prostate: a clinicopathologic study of 29 cases. Am J Surg Pathol 2007;31:697-705. [13] Nordkvist A, Mark J, Gustafsson H, Bang G, Stenman G. Nonrandom chromosome rearrangements in adenoid cystic carcinoma of the salivary glands. Genes Chromosomes Cancer 1994;10: 115-21. [14] Persson M, Andren Y, Mark J, Horlings HM, Persson F, Stenman G. Recurrent fusion of MYB and NFIB transcription factor genes in carcinomas of the breast and head and neck. Proc Natl Acad Sci U S A 2009;106:18740-4.
J. A. Bishop et al. [15] Fehr A, Kovacs A, Loning T, Frierson Jr H, van den Oord J, Stenman G. The MYB-NFIB gene fusion – a novel genetic link between adenoid cystic carcinoma and dermal cylindroma. J Pathol 2011;224: 322-7. [16] Tomlins SA, Laxman B, Dhanasekaran SM, et al. Distinct classes of chromosomal rearrangements create oncogenic ETS gene fusions in prostate cancer. Nature 2007;448:595-9. [17] Persson M, Andren Y, Moskaluk CA, et al. Clinically significant copy number alterations and complex rearrangements of MYB and NFIB in head and neck adenoid cystic carcinoma. Genes Chromosomes Cancer 2012;51:805-17. [18] Behboudi A, Enlund F, Winnes M, et al. Molecular classification of mucoepidermoid carcinomas-prognostic significance of the MECT1MAML2 fusion oncogene. Genes Chromosomes Cancer 2006;45:470-81. [19] Okabe M, Miyabe S, Nagatsuka H, et al. MECT1-MAML2 fusion transcript defines a favorable subset of mucoepidermoid carcinoma. Clin Cancer Res 2006;12:3902-7. [20] Skalova A, Vanecek T, Sima R, et al. Mammary analogue secretory carcinoma of salivary glands, containing the ETV6-NTRK3 fusion gene: a hitherto undescribed salivary gland tumor entity. Am J Surg Pathol 2010;34:599-608. [21] Mitani Y, Li J, Rao PH, et al. Comprehensive analysis of the MYBNFIB gene fusion in salivary adenoid cystic carcinoma: Incidence, variability, and clinicopathologic significance. Clin Cancer Res 2010; 16:4722-31. [22] Mitani Y, Rao PH, Futreal PA, et al. Novel chromosomal rearrangements and break points at the T(6;9) in salivary adenoid cystic carcinoma: Association with MYB-NFIB chimeric fusion, MYB expression, and clinical outcome. Clin Cancer Res 2011;17: 7003-14. [23] West RB, Kong C, Clarke N, et al. MYB expression and translocation in adenoid cystic carcinomas and other salivary gland tumors with clinicopathologic correlation. Am J Surg Pathol 2011;35:92-9. [24] Reed RJ. Consultation case: prostate (prostatectomy)–adenoid basalcell tumor–multifocal basal-cell hyperplasia. Am J Surg Pathol 1984; 8:699-704. [25] Young RH, Frierson Jr HF, Mills SE, Kaiser JS, Talbot WH, Bhan AK. Adenoid cystic-like tumor of the prostate gland. A report of two cases and review of the literature on “adenoid cystic carcinoma" of the prostate. Am J Clin Pathol 1988;89:49-56. [26] Stenman G. Fusion oncogenes in salivary gland tumors: Molecular and clinical consequences. Head Neck Pathol 2013;7(Suppl 1):S12-9.
www.elsevier.com/locate/humpath
Original contribution
A subset of prostatic basal cell carcinomas harbor the MYB rearrangement of adenoid cystic carcinoma☆,☆☆ Justin A. Bishop MD a,b,⁎, Raluca Yonescu MD a , Jonathan I. Epstein MD a,c,d , William H. Westra MD a,b,c a
Department of Pathology, The Johns Hopkins Medical Institutions, Baltimore, MD 21231 Department of Otolaryngology/Head and Neck Surgery, The Johns Hopkins Medical Institutions, Baltimore, MD 21231 c Department of Urology, The Johns Hopkins Medical Institutions, Baltimore, MD 21231 d Department of Oncology, The Johns Hopkins Medical Institutions, Baltimore, MD 21231 b
Received 10 February 2015; revised 1 May 2015; accepted 7 May 2015
Keywords: Prostate; Adenoid cystic carcinoma; Basal cell carcinoma; MYB-NFIB; Fluorescence in situ hybridization
Summary Adenoid cystic carcinoma (ACC) is a basaloid tumor consisting of myoepithelial and ductal cells typically arranged in a cribriform pattern. Adenoid cystic carcinoma is generally regarded as a form of salivary gland carcinoma, but it can arise from sites unassociated with salivary tissue. A rare form of prostate carcinoma exhibits ACC-like features; it is no longer regarded as a true ACC but rather as prostatic basal cell carcinoma (PBCC) and within the spectrum of basaloid prostatic proliferations. True ACCs often harbor MYB translocations resulting in the MYB-NFIB fusion protein. MYB analysis could clarify the true nature of prostatic carcinomas that exhibit ACC features and thus help refine the classification of prostatic basaloid proliferations. Twelve PBCCs were identified from the pathology consultation files of Johns Hopkins Hospital. The histopathologic features were reviewed, and breakapart fluorescence in situ hybridization for MYB was performed. All 12 cases exhibited prominent basaloid histology. Four were purely solid, 7 exhibited a cribriform pattern reminiscent of salivary ACC, and 1 had a mixed pattern. The MYB rearrangement was detected in 2 (29%) of 7 ACC-like carcinomas but in none (0%) of the 5 PBCCs with a prominent solid pattern. True ACCs can arise in the prostate as is evidenced by the presence of the characteristic MYB rearrangement. When dealing with malignant basaloid proliferations in the prostate, recommendations to consolidate ACCs with other tumor types may need to be reassessed, particularly in light of the rapidly advancing field of biologic therapy where the identification of tumor-specific genetic alterations presents novel therapeutic targets. © 2015 Elsevier Inc. All rights reserved.
1. Introduction ☆
Competing interests: The authors have no conflicts of interest to declare. Funding/Support: This study was funded in part by the National Institutes of Health/National Institute of Dental and Craniofacial Research (NIH/NIDCR) Head and Neck SPORE Grant P50 DE019032. ⁎ Corresponding author at: The Johns Hopkins University School of Medicine, 401 N. Broadway, Weinberg 2249, Baltimore, MD 21231. E-mail address: [email protected] (J. A. Bishop). ☆☆
http://dx.doi.org/10.1016/j.humpath.2015.05.002 0046-8177/© 2015 Elsevier Inc. All rights reserved.
Adenoid cystic carcinoma (ACC) is a salivary gland tumor that is composed of ductal and myoepithelial cells. Adenoid cystic carcinoma can also arise in sites unassociated with salivary gland tissue including the skin, cervix, and breast [1-5]. The existence of a prostatic form of ACC is controversial. At one time recognized by the World Health
MYB rearrangements in prostatic basal cell carcinomas Organization (WHO) classification of prostatic tumors as a true tumor entity [6], prostatic ACC has since been discarded as a diagnostic category in more recent WHO classification schemes [7]. This reconsideration was prompted by 2 observations. First, myoepithelial cells are not indigenous to the prostate such that a myoepithelial form of prostatic carcinoma is entirely unanticipated at this site. Second, the adenoid cystic morphology occurs along a spectrum of basaloid proliferations that encompasses basal cell hyperplasia, basal cell adenoma, and basal cell basal cell carcinoma [8-12]. Accordingly, current WHO classification has combined ACC with other malignant basaloid tumors of the prostate under the single term basal cell carcinoma, at least until studies can establish a more compelling link to true ACC than mere phenotypic similarities [7]. Recent studies have shown that ACCs often harbor a recurrent t(6;9)(q22-23;p23-24) translocation resulting in a novel fusion of the MYB proto-oncogene with the NFIB transcription factor gene [13,14]. The fusion is not detected in non-ACCs, but its consistent presence in ACCs across various anatomical sites including salivary gland, sinonasal cavity, tracheobronchial tree, larynx, breast, and vulva clearly links the adenoid cystic phenotype with a specific molecular pathway [1,14,15]. Toward that end, we evaluated prostatic basal cell carcinoma (PBCCs) for the presence of the MYB-NFIB translocation to determine if this defining genetic alteration could help refine the classification of this controversial group of tumors.
2. Materials and methods This study was approved by The Johns Hopkins Institutional Review Board (IRB05070101). Histologic slides and paraffin-embedded tissue blocks from 12 PBCCs were retrieved from the surgical pathology consultation files of 1 of the authors (J.I.E.). Fluorescence in situ hybridization was performed on formalin-fixed, paraffin-embedded sections using a commercially available MYB dual-color break-apart probe (ZTV-Z-2143-200, ZytoVision, Bremerhaven, Germany). The probe was designed to detect translocations involving the chromosomal region 6q23.3 harboring the MYB gene. Before hybridization, the slides were deparaffinized using a VP 2000 processor (Abbott Molecular, Des Plains, IL). The slides and the MYB probe were codenatured at 80°C for 7 minutes and allowed to anneal over night at 37°C in humidified atmosphere. At the end of the incubation, the slides were washed in 2× SSC/ 0.3% NP-40 for 2 minutes at 72°C and for 2 minutes at room temperature in 2× SSC. The slides were counterstained with DAPI, and a cover slip was applied using Vectashield mounting medium (H-1000, Vector Laboratories, Inc., Burlingame, CA). A fluorescence microscope was used to evaluate the probe pattern. Cells with 2 fusion signals of 1 orange and 1 green fluorochrome were scored as normal and considered negative for MYB break apart (MYB negative). A signal pattern consisting of 1 fusion signal and 1 orange and 1 green signal
1205 at distance from each other indicated 1 normal 6q23.3 locus and 1 locus affected by a translocation.
3. Results All cases were transurethral resections of the prostate. The patients ranged in age from 65 to 86 years (mean, 72 years). Notably, none of the patients had a known history of prior head and neck carcinoma. The morphological features of the tumors are summarized in the Table. Each tumor exhibited overtly infiltrative growth and shared prominent basaloid morphology, but there existed a spectrum of histologic changes. Four tumors (25%) exhibited tumor necrosis, and 2 (17%) demonstrated perineural invasion. Seven cases (54%) (cases 1-7) exhibited morphological findings highly reminiscent of ACC (Fig. 1A), whereas 4 cases (33%) (cases 9-12) consisted purely of solid nests of basaloid cells and did not resemble ACC closely (Fig. 1B). The ACC-like tumors demonstrated a biphasic pattern consisting of varying proportions of basaloid cribriform structures and nests admixed with centrally located tubules with eosinophilic cytoplasm (Fig. 1A, C, D). The eosinophilic tubules were generally abundant, but in 2 cases (cases 4 and 5), they were relatively focal and indistinct. One of these ACC-like cases (case 6) also contained pseudocystic spaces filled with basement membrane material (Fig. 1A), and in case 3, the eosinophilic tubules exhibited cytoplasmic vacuolization. In contrast, the solid-patterned carcinomas showed no cribriforming or tubular structures (Fig. 1B). Of these solid-patterned carcinomas, 3 demonstrated areas of comedonecrosis within some of the tumor nests. Finally, 1 tumor (case 8) had a mixed pattern; it grew predominantly as zones of solid nests but also demonstrated focal areas of biphasic growth with nests admixed with eosinophilic tubules (Fig. 1E and F). Overall, 2 (17%) of 12 PBCCs were positive for a MYB rearrangement by fluorescence in situ hybridization (Figs. 2 and 3). The positive cases were restricted to the adenoid cystic-like basal cell carcinomas without solid growth (2/7, 29%) (Fig. 2). One of the MYB-rearranged cases (case 5) exhibited a purely cribriform growth pattern (Fig. 2A), whereas the other case (case 1) had mixed tubular and cribriform features (Fig. 2B). In contrast, the MYB rearrangement was not identified in any of the 5 basal cell carcinomas that were entirely or predominantly solid in pattern. Of the 2 MYB-rearranged cases, 1 exhibited perineural invasion compared with 1 of 10 cases without MYB rearrangements.
4. Discussion Chromosome rearrangements, in particular translocations, may result in fusion oncogenes encoding oncoproteins with transforming properties. Most gene fusions are found in leukemias and sarcomas, but several carcinomas have also
1206
J. A. Bishop et al.
Table
The histopathologic and molecular features of 12 PBCCs
Case
Microscopic features
MYB rearrangement
1 2 3 4 5 6 7 8 9 10 11 12
Basaloid nests and cribriform glands with abundant central eosinophilic tubules Basaloid nests and cribriform glands with abundant central eosinophilic tubules Basaloid nests and cribriform glands with abundant central eosinophilic and vacuolated tubules Basaloid nests and cribriform glands with indistinct eosinophilic tubules Cribriform glands with indistinct eosinophilic tubules Basaloid nests and cribriform glands with abundant central eosinophilic tubules and pseudocystic spaces Basaloid nests and cribriform glands with abundant central eosinophilic tubules Predominantly solid basaloid nests, with areas of nests containing central eosinophilic tubules Solid basaloid nests Solid basaloid nests with necrosis Solid basaloid nests with necrosis Solid basaloid nests with necrosis
+ − − − + − − − − − − −
been shown to express fusion oncogenes. Most notably, the ETS and TMPRRS2 fusions are found in most prostate carcinomas [16]. Several gene fusions have also been identified in salivary
gland neoplasms [17-20]. As one important example, ACCs often harbor a recurrent t(6;9)(q22-23;p23-24) translocation resulting in a fusion of the MYB oncogene to the transcription
Fig. 1 The prostate basal cell carcinomas ranged from tubular and cribriform (A) to purely solid (B) in architecture. Most of the tubular and cribriform carcinomas (C and D) also exhibited numerous central ducts with eosinophilic cytoplasm. One basal cell carcinoma had mixed features, with areas of both tubular (E) and solid (F) growth. (For each, hematoxylin and eosin, original magnification ×40).
MYB rearrangements in prostatic basal cell carcinomas
1207
Fig. 2 The 2 carcinomas that harbored MYB rearrangements had histologic features that were highly reminiscent of adenoid cystic carcinoma of salivary glands. One case showed a predominantly cribriform growth pattern (A), whereas the other case had a mixed tubular and cribriform appearance (B). (For each, hematoxylin and eosin, ×40).
factor gene NFIB [1,13,14]. The MYB-NFIB fusion has not been found in any non-ACC carcinomas, such that its detection may be exploited as a diagnostic biomarker for identifying ACC in the head and neck and other sites. Our results show that a subset of PBCCs harbors rearrangement of MYB. The MYB rearrangement was limited to those PBCCs that closely resembled salivary gland ACC. The presence of a specific genetic link with ACC supports the early but discarded view that a subset of PBCCs does represent a true form of ACC. Although the MYB rearrangement was not present in all of the prostatic carcinomas with an adenoid cystic-like morphology, its incidence (29%) falls within the range reported for ACCs of the head and neck (28%-49%) [1,17,21-23]. Moreover, its absence in purely or predominantly solid basal cell carcinomas casts some doubt on the current classification scheme that views all basaloid carcinomas of the prostate as single tumor type. Prostatic basal cell carcinoma is very rare (n = 29 in the largest series) [12], and it is difficult to make definitive conclusions based on our relatively limited number of cases. If, however, our findings are replicated on additional cases of PBCC, classification schemes of primary prostatic carcinomas may need to be modified to again
recognize ACC as a specific entity that warrants separation from the solid basal cell carcinoma. Once regarded as an indolent tumor based on small case numbers with short follow-up [24,25], larger studies with longer follow-up have disclosed that the behavior of PBCCs with adenoid cystic-like features is quite in keeping with ACC including infiltrative growth, local recurrence, metastatic spread to distant sites, and patient death [8-11]. Although ACCs are notoriously unresponsive to conventional chemotherapy, recognition of an activated genetic pathway now opens the way for directed therapy regardless of tumor origin. In the MYB-NFIB fusion oncogene, the 3′ end of MYB, including target sites for negatively regulating microRNAs, is replaced by 1 or more of the coding exons of NFIB [26]. The predicted MYB-NFIB fusion protein retains the DNA binding and transactivation domains of MYB and can activate various genes regulating cell growth and differentiation including BCL2, KIT, CD34, BIRC3, MYC, and MAD1L1. In effect, more accurate refinement of prostatic basaloid neoplasms is more than just a nosologic triviality but may help tailor treatment based on an association of tumor phenotype with an activated genetic pathway that includes various potential therapeutic targets.
Fig. 3 This tumor (case 1) had an ACC-like appearance (A) (hematoxylin and eosin, ×400) and harbored a MYB rearrangement as indicated by the red and greed signals on this break-apart fluorescent in situ hybridization assay (B).
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