Brush Cytology of Acinar Cell Carcinoma of the Pancreas With Intraductal Growth: A Case Report Yasuhiro Toyonaga, C.T.,1 Kazuto Yamazaki, M.D., Ph.D.,1 Masatoshi Yamada, M.D.,1,2 Takayoshi Koyasu, C.T.,1 Yoshinori Koyama, C.T.,1 and Yasuo Ishida, M.D., Ph.D.1
We describe a rare case of pancreatic acinar cell carcinoma (ACC) with intraductal growth in a 77-year-old man, which was diagnosed by endoscopic brush cytology. Preoperative imaging revealed an ill-defined mass involving the main pancreatic duct of the body, which was suspected to be an invasive ductal carcinoma. Endoscopic brush cytology showed several thick, small to large clusters of tumor cells. However, a loosely cohesive or individual cell arrangement was more prominent. Singly dispersed naked nuclei, occasionally with crush artifact, were frequently observed. The nuclear contour was smooth and chromatin was finely clumped. The cytoplasm contained many coarse D-PAS-positive granules. Histologically, the tumor expansively invaded to parenchyma and expanded to fill the pancreatic ducts. Ultrastructurally, the tumor cells were less cohesive with scarce tight junctions, and their cytoplasm contained numerous zymogen granules and filamentous inclusions. Although ACCs usually show expansive growth, the incidence of intraductal extension may be higher than previously considered. A few of the characteristic cytomorphological features described here may be useful for differential diagnosis of this tumor from malignant epithelioid neoplasms involving the large pancreatic ducts. Diagn. Cytopathol. 2014;42:321–324. VC 2013 Wiley Periodicals, Inc. Key Words: pancreas; acinar cell carcinoma; intraductal growth; brush cytology
1 Department of Pathology, Teikyo University, Chiba Medical Center, Ichihara, Japan 2 Department of Molecular Pathology, Tokyo Medical University, Shinjuku, Japan *Correspondence to: Kazuto Yamazaki, M.D., Ph.D., Department of Pathology, Teikyo University, Chiba Medical Center, 3426-3 Anesaki, Ichihara, Chiba, 299-0111, Japan. E-mail: [email protected] Received 29 August 2013; Accepted 3 December 2013 DOI: 10.1002/dc.23087 Published online 20 December 2013 in Wiley Online Library (wileyonlinelibrary.com).
C 2013 WILEY PERIODICALS, INC. V
Introduction Acinar cell carcinoma (ACC) is uncommon, accounting for 1–2% of all pancreatic exocrine tumors.1–3 The 5-year survival rate for patients with ACC is not favorable (5– 10%), but slightly better than that of patients with pancreatic ductal carcinomas (PDCs).2 Grossly, most ACCs are large and rather well circumscribed, sometimes being partly encapsulated.1–3 However, they can extensively invade into adjacent tissue and only 50% of the tumors appear to be resectable at the time of diagnosis.4 Accurate distinction of ACC from other neoplasms is important for treatment planning, because neoadjuvant chemotherapy may be an option for reduction of a primarily unresectable ACC to a point where curative resection can be achieved.4 ACCs usually show expansive growth, and involvement of the biliary or pancreatic duct is rare in comparison with PDCs.5 As they are not usually accessible for endoscopic brush cytology, diagnosis is often established from cytology specimens collected via fine-needle aspiration (FNA).5,6 Several reports have described a rare intraductal variant of ACC showing papillary growth of tumor cells predominantly within dilated pancreatic ducts.7,8 Moreover, a recent study has indicated that conventional nodular ACC occasionally shows extensive growth within large pancreatic ducts, although the tumor cells in the nodular areas show either a solid or an acinar pattern.9 However, because of its rarity, the cytomorphological features that can be used for accurate diagnosis of ACC with intraductal growth have not yet been investigated. Here, we describe a case of ACC showing predominantly nodular growth, destructive involvement of the main pancreatic duct, and extension into the branch ducts, for which sampling of the tumor cells by endoscopic brush cytology was possible. Diagnostic Cytopathology, Vol. 42, No 4
321
Diagnostic Cytopathology DOI 10.1002/dc
TOYONAGA ET AL.
Fig. 1. A: Abdominal enhanced CT scan shows a ill-delineated slightly enhanced tumor (arrows) in the body of the pancreas and dilation of the distal main pancreatic duct. B: MRCP reveals a blocked main pancreatic duct in the body of the pancreas (arrows).
Case Reports Clinical History A 77-year-old male with a history of excessive alcohol intake was referred to our institution because of continuous abdominal pain. The patient had not experienced any recent weight loss or jaundice. Abdominal CT and MRI with contrast enhancement revealed an ill-defined slightly enhanced tumor in the body of the pancreas and dilatation of the distal main pancreatic duct (Fig. 1A). Magnetic resonance cholangiopancreatography also revealed a blocked main pancreatic duct in the body of the pancreas (Fig. 1B). Endoscopic brush cytology of the main pancreatic duct was performed. We preoperatively interpreted this neoplasm as “adenocarcinoma with predominant acinar differentiation.” Distal pancreatectomy and splenectomy were performed. The resected pancreatic specimen showed diffuse swelling of the pancreas body and no obvious surface invasion. The cut surface revealed a whitish ill-defined mass (measuring 3.0 3 1.6 3 1.0 cm3) with parenchymal invasion and involvement of the main pancreatic duct. On the basis of the histological findings, this case was diagnosed as ACC, T2N0M0, according to the UICC TNM classification. Although the resection was curative, the patient was readmitted because of bone metastasis 29 months after the operation. He has been receiving chemotherapy and is currently alive 48 months after surgery.
Cytological and Histological Findings Papanicolaou- and Giemsa-stained smears showed several thick, small to large clusters of tumor cells (Fig. 2A); however, a loosely cohesive or individual cell arrangement was more prominent (Fig. 2B). The smear background contained abundant coarse cytoplasmic particles that had been stripped from the tumor cells (Fig. 2C). There were abundant dissociated naked tumor nuclei, some of which revealed crush artifacts. Typically, the tumor cells were polygonal with a low nucleus to cyto322
Diagnostic Cytopathology, Vol. 42, No 4
Fig. 2. A: Smears of endoscopic brush cytology show large clusters with nuclear overlapping. B: Loose trabecular clusters and individual tumor cells. C: Abundant dissociated naked nuclei, some of which reveal crush artifacts. The smear background contains abundant stripped cytoplasmic particles. Papanicolaou stain, 3200 (A), 3600 (B), and 3400 (C). D: The tumor cells (arrows) contain D-PAS positive cytoplasmic granules. Benign ductal cells (arrow heads) show diffuse cytoplasmic staining. D-PAS stain, 3400. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
plasm ratio and uniform nuclei with a smooth contour and finely clumped chromatin. The nuclei had one or two prominent nucleoli and the cytoplasm was dense and granular. Approximately, 50% of the tumor cells contained numbers of round or fusiform coarse granules that were positive for diastase-digested periodic acid-Schiff reaction (D-PAS) (Fig. 2D). Histologically, the tumor nests showed a solid or large trabecular pattern comprising a monotonous population of cells arranged in solid sheets or an acinar pattern with a delicate fibrovascular network. The tumor nests had expansively invaded into the parenchyma, disrupting the wall of the main pancreatic duct, and expanding to fill the branch ducts (Fig. 3A). Microscopic venous invasion was also
Diagnostic Cytopathology DOI 10.1002/dc
CYTOLOGY OF INTRADUCTAL ACC OF THE PANCREAS
Fig. 3. A: The tumor expand to fill the branch ducts. Non-tumorous epithelial cells are seen covering the ductal lumen. Hematoxylin-eosion stain, 3200. B: The tumor cells contain D-PAS-positive granules in their cytoplasm. D-PAS stain, 3400. C: Immunohistochemically, the tumor cells are positive for trypsin. 3400. D: Electron microscopy shows the tumor cells contain round zymogen granules and filamentous inclusions in their cytoplasm. 320,000. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
noted, but no invasion to lymphatic vessels or metastasis to peripancreatic lymph nodes was evident. The cytoplasm contained D-PAS-positive granules in the apical region (Fig. 3B). Immunohistochemically, the tumor cells showed extensive expression of trypsin, a known acinar cell marker (Fig. 3C), and a1-antitrypsin. Scattered individual tumor cells were positive for synaptophysin and chromogranin. Overall, the tumor cells were negative for amylase, insulin, glucagon, somatostatin, CEA, CA19–9, CD10, and CD56. Nuclear expression of p16 and DPC4 was well conserved and nuclear accumulation of p53 and b-catenin was not evident. Ultrastructurally, the tumor cells were less cohesive, having wide intercellular spaces. Desmosomal and tight junctions were scarce. The nuclei were basally oriented and the cytoplasm contained abundant dilated rough endoplasmic reticulum, mitochondria, and two types of large inclusions: round (200–600 nm in diameter) zymogen granules of uniform density and filamentous inclusions (250–800 nm in diameter, up to 3,500 nm long) with fibrillary internal structures (Fig. 3D).
Discussion Accurate diagnosis of pancreatic neoplasm is essential for planning therapies such as surgery, endoscopy, or alternative treatments. Endoscopic brush cytology is one of the most reliable methods for diagnosis of PDCs, which account for the majority of pancreatic neoplasms. They originate in the pancreatic ductal epithelium, generally show infiltrative growth, and often invade and obstruct the large pancreatic ducts. PDCs tend to extend along the
pancreatic ducts, replacing the luminal epithelium, and are often diagnosed by brush cytology.9 In contrast, ACC is usually a solid tumor showing expansive growth, and intraductal growth is quite rare.7–9 Therefore, there is a high probability that pancreatic brush cytology will misdiagnose duct-infiltrative ACC as PDC. In fact, this case was suspected to be PDC on the basis of preoperative imaging. However, its cytomorphological features did not resembled PDC, as the tumor cells had uniform nuclei with a smooth contour, finely clumped chromatin, and dense granular cytoplasm.1,5 In contrast, well differentiated PDC usually shows a “drunken honeycomb” arrangement with an uneven cell distribution, some nuclear overlapping, and variation of nuclear size.1 In poorly differentiated PDC, nuclear pleomorphism and nuclear contour abnormalities are more evident. Furthermore, the tumor cells of PDC contain abundant mucin, often identifiable even by Papanicolaou staining, and their cytoplasm is diffusely D-PAS-positive.1 Cytologically, ACC can mimic pancreatic neuroendocrine tumor (PanNET) and solid-pseudopapillary neoplasm (SPPN).1,2 In fact, these tumor cells commonly have round to oval nuclei and granular cytoplasm, as is the case in ACC.5 However, the nuclei of PanNET usually show a coarsely granular, so-called “salt-and-pepper” chromatin distribution, unlike the tumor cells in this case. Meanwhile, SPPNs commonly show prominent nuclear grooves, hyaline globules with delicate fibrovascular cores and a myxoid stroma. Moreover, the background may be filled with hemorrhagic cyst debris laden with foamy histiocytes and multinucleated giant cells,1,5 which were not observed in this case. Essentially, both PanNET and SPPN are commonly discrete, well circumscribed tumors showing expansive growth. Although they occasionally compress or narrow the large pancreatic duct, blockage of the duct and intraductal extension seem to be rare.9 Intraductal extension is also rare in ACCs, but several reports have indicated that an intraductal variant of ACC exhibits predominantly intraductal polypoid growth in the large pancreatic ducts.7,8 Recently, Ban et al. reviewed the histologic features of 13 case of ACC, of which 7 (54%) showed intraductal polypoid growth of the tumor in the large pancreatic ducts. Among them, four cases showed predominant intraductal tumor growth with a "sausage-like" shape, but the other three cases showed intraductal polypoid growth as well as nodular lesions with expansive invasion, as was seen in this case.9 In both intraductal and nodular lesions, tumor cells proliferated in a solid or acinar pattern with a scant stromal component. Therefore, the pancreatic ducts are an important route of tumor extension, not only for the predominantly intraductal variant but also for conventional ACC, and brush cytology may be a reliable diagnostic method for them. Ultrastructurally, ACCs often contain numerous large cytoplasmic granules, known as zymogen granules, and Diagnostic Cytopathology, Vol. 42, No 4
323
Diagnostic Cytopathology DOI 10.1002/dc
TOYONAGA ET AL.
filamentous inclusions that are thought to lie within the spectrum of zymogen granules.10,11 These inclusions are present in primary pancreatic tumors, particularly pure ACC, but less frequently in mixed acinar-endocrine carcinoma. They have only rarely been identified in PanNET, and have never been reported in SPPN.12,13 Therefore, the presence of these inclusions may serve as an ultrastructural marker of cells showing acinar differentiation. Zymogen granules are known to be PAS-positive and diastase-resistant.3 Certainly not all ACCs have these inclusions, and some tumor cells in this case showed only a sparse distribution of zymogen granules. However, the presence of tumor cells with coarse D-PAS-positive cytoplasmic granules may indicate acinar differentiation.3 Although the common cytoarchitecture of ACC in FNA specimen is small to large, thick, and 3-dimensional clusters with prominent acinar formation, recent studies of FNA reported that abundant stripped nuclei were found at periphery of the loose clusters as our present case.5,6 This discohesive cytoarchitecture, common to both of FNA and brush cytology, may reflect the histological characteristics of ACC; lack of intervening stroma, weak cohesion, and fragility of the tumor cells.14 However, the cytological specimens of our case seemed to be more discohesive than FNA specimens of the previous studies. In addition, some stripped nuclei with crush artifact and abundant cytoplasmic particles observed in our case, that have not noted in the prior studies of FNA specimens, may reflect the artifacts of the brushing during sampling. In summary, we have presented a case of pancreatic ACC with intraductal growth, which was diagnosed by endoscopic brush cytology. It is important to be aware of the characteristics revealed by brush cytology, especially as the incidence of intraductal extension of ACC may be higher than previously considered, and there may be important prognostic and therapeutic implications for the patient. Although a helpful immunohistochemical panel may be necessary in some cases,13–15 a few of the characteristic cytomorphological features described here may be useful for differential diagnosis of ACC from malignant epithelioid neoplasms involving the large pancreatic ducts.
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References 1. Hruban RH, Klimstra DS, Pitman MB. Tumors of the pancreas. Atlas of tumor pathology. 4th series. Washington DC: Armed Forces Institute of Pathology; 2006. 2. Klimstra DS, Heffess CS, Oertel JE, Rosai J. Acinar cell carcinoma of the pancreas. A clinicopathologic study of 28 cases. Am J Surg Pathol 1992;16:815–837. ~ez NG. Pancreatic acinar cell carcinoma. Adv Anat Pathol 3. Ord on 2001;8:144–159. 4. Distler M, R€ uckert F, Dittert DD, Stroszczynski C, Dobrowolski F, Kersting S, Gr€ utzmann R. Curative resection of a primarily unresectable acinar cell carcinoma of the pancreas after chemotherapy. World J Surg Oncol 2009;7:7–22. 5. Sigel CS, Klimstra DS. Cytomorphologic and immunophenotypical features of acinar cell neoplasms of the pancreas. Cancer Cytopathol 2013;121:459–470. 6. Stelow EB, Bardales RH, Shami VM, Woon C, Presley A, Mallery S, Lai R, Stanley MW. Cytology of pancreatic acinar cell carcinoma. Diagn Cytopathol 2006;34:367–372. 7. Fabre A, Sauvanet A, Flejou JF, Belghiti J, Palazzo L, Ruszniewski P, Degott C, Terris B. Intraductal acinar cell carcinoma of the pancreas. Virchows Arch 2001;438:312–315. 8. Basturk O, Zamboni G, Klimstra DS, Capelli P, Andea A, Kamel NS, Adsay NV. Intraductal and papillary variants of acinar cell carcinomas: A new addition to the challenging differential diagnosis of intraductal neoplasms. Am J Surg Pathol 2007;31:363–370. 9. Ban D, Shimada K, Sekine S, Sakamoto Y, Kosuge T, Kanai Y, Hiraoka N. Pancreatic ducts as an important route of tumor extension for acinar cell carcinoma of the pancreas. Am J Surg Pathol 2010;34:1025–1036. 10. Tucker JA, Shelburne JD, Benning TL, Yacoub L, Federman M. Filamentous inclusions in acinar cell carcinoma of the pancreas. Ultrastruct Pathol 1994;18:279–286. 11. Chong JM, Fukayama M, Shiozawa Y, Hayashi Y, Funata N, Takizawa T, Koike M. Fibrillary inclusions in tumor and fetal acinar cells of the pancreas. Virchows Arch 1996;428:261–266. 12. Horie A, Morohashi T, Kloppel G. Ultrastructural comparison of pancreatoblastoma, solid cystic tumor and acinar cell carcinoma. J Clin Electron Microscopy 1987;20:353–362. 13. Morohoshi T, Kanda M, Horie A, et al. Immunohistochemical markers of uncommon pancreatic tumors: Acinar cell carcinoma, pancreatoblastoma, and solid cystic (papillary-cystic) tumor. Cancer 1987;59:739–747. 14. Toll AD, Hruban RH, Ali SZ. Acinar cell carcinoma of the pancreas: Clinical and cytomorphologic characteristics. Kor J Pathol 2013;47:93–99. 15. Hosoda W, Sasaki E, Murakami Y, Yamao K, Shimizu Y, Yatabe Y. BCL10 as a useful marker for pancreatic acinar cell carcinoma, especially using endoscopic ultrasound cytology specimens. Pathol Int 2013;63:176–182.
We describe a rare case of pancreatic acinar cell carcinoma (ACC) with intraductal growth in a 77-year-old man, which was diagnosed by endoscopic brush cytology. Preoperative imaging revealed an ill-defined mass involving the main pancreatic duct of the body, which was suspected to be an invasive ductal carcinoma. Endoscopic brush cytology showed several thick, small to large clusters of tumor cells. However, a loosely cohesive or individual cell arrangement was more prominent. Singly dispersed naked nuclei, occasionally with crush artifact, were frequently observed. The nuclear contour was smooth and chromatin was finely clumped. The cytoplasm contained many coarse D-PAS-positive granules. Histologically, the tumor expansively invaded to parenchyma and expanded to fill the pancreatic ducts. Ultrastructurally, the tumor cells were less cohesive with scarce tight junctions, and their cytoplasm contained numerous zymogen granules and filamentous inclusions. Although ACCs usually show expansive growth, the incidence of intraductal extension may be higher than previously considered. A few of the characteristic cytomorphological features described here may be useful for differential diagnosis of this tumor from malignant epithelioid neoplasms involving the large pancreatic ducts. Diagn. Cytopathol. 2014;42:321–324. VC 2013 Wiley Periodicals, Inc. Key Words: pancreas; acinar cell carcinoma; intraductal growth; brush cytology
1 Department of Pathology, Teikyo University, Chiba Medical Center, Ichihara, Japan 2 Department of Molecular Pathology, Tokyo Medical University, Shinjuku, Japan *Correspondence to: Kazuto Yamazaki, M.D., Ph.D., Department of Pathology, Teikyo University, Chiba Medical Center, 3426-3 Anesaki, Ichihara, Chiba, 299-0111, Japan. E-mail: [email protected] Received 29 August 2013; Accepted 3 December 2013 DOI: 10.1002/dc.23087 Published online 20 December 2013 in Wiley Online Library (wileyonlinelibrary.com).
C 2013 WILEY PERIODICALS, INC. V
Introduction Acinar cell carcinoma (ACC) is uncommon, accounting for 1–2% of all pancreatic exocrine tumors.1–3 The 5-year survival rate for patients with ACC is not favorable (5– 10%), but slightly better than that of patients with pancreatic ductal carcinomas (PDCs).2 Grossly, most ACCs are large and rather well circumscribed, sometimes being partly encapsulated.1–3 However, they can extensively invade into adjacent tissue and only 50% of the tumors appear to be resectable at the time of diagnosis.4 Accurate distinction of ACC from other neoplasms is important for treatment planning, because neoadjuvant chemotherapy may be an option for reduction of a primarily unresectable ACC to a point where curative resection can be achieved.4 ACCs usually show expansive growth, and involvement of the biliary or pancreatic duct is rare in comparison with PDCs.5 As they are not usually accessible for endoscopic brush cytology, diagnosis is often established from cytology specimens collected via fine-needle aspiration (FNA).5,6 Several reports have described a rare intraductal variant of ACC showing papillary growth of tumor cells predominantly within dilated pancreatic ducts.7,8 Moreover, a recent study has indicated that conventional nodular ACC occasionally shows extensive growth within large pancreatic ducts, although the tumor cells in the nodular areas show either a solid or an acinar pattern.9 However, because of its rarity, the cytomorphological features that can be used for accurate diagnosis of ACC with intraductal growth have not yet been investigated. Here, we describe a case of ACC showing predominantly nodular growth, destructive involvement of the main pancreatic duct, and extension into the branch ducts, for which sampling of the tumor cells by endoscopic brush cytology was possible. Diagnostic Cytopathology, Vol. 42, No 4
321
Diagnostic Cytopathology DOI 10.1002/dc
TOYONAGA ET AL.
Fig. 1. A: Abdominal enhanced CT scan shows a ill-delineated slightly enhanced tumor (arrows) in the body of the pancreas and dilation of the distal main pancreatic duct. B: MRCP reveals a blocked main pancreatic duct in the body of the pancreas (arrows).
Case Reports Clinical History A 77-year-old male with a history of excessive alcohol intake was referred to our institution because of continuous abdominal pain. The patient had not experienced any recent weight loss or jaundice. Abdominal CT and MRI with contrast enhancement revealed an ill-defined slightly enhanced tumor in the body of the pancreas and dilatation of the distal main pancreatic duct (Fig. 1A). Magnetic resonance cholangiopancreatography also revealed a blocked main pancreatic duct in the body of the pancreas (Fig. 1B). Endoscopic brush cytology of the main pancreatic duct was performed. We preoperatively interpreted this neoplasm as “adenocarcinoma with predominant acinar differentiation.” Distal pancreatectomy and splenectomy were performed. The resected pancreatic specimen showed diffuse swelling of the pancreas body and no obvious surface invasion. The cut surface revealed a whitish ill-defined mass (measuring 3.0 3 1.6 3 1.0 cm3) with parenchymal invasion and involvement of the main pancreatic duct. On the basis of the histological findings, this case was diagnosed as ACC, T2N0M0, according to the UICC TNM classification. Although the resection was curative, the patient was readmitted because of bone metastasis 29 months after the operation. He has been receiving chemotherapy and is currently alive 48 months after surgery.
Cytological and Histological Findings Papanicolaou- and Giemsa-stained smears showed several thick, small to large clusters of tumor cells (Fig. 2A); however, a loosely cohesive or individual cell arrangement was more prominent (Fig. 2B). The smear background contained abundant coarse cytoplasmic particles that had been stripped from the tumor cells (Fig. 2C). There were abundant dissociated naked tumor nuclei, some of which revealed crush artifacts. Typically, the tumor cells were polygonal with a low nucleus to cyto322
Diagnostic Cytopathology, Vol. 42, No 4
Fig. 2. A: Smears of endoscopic brush cytology show large clusters with nuclear overlapping. B: Loose trabecular clusters and individual tumor cells. C: Abundant dissociated naked nuclei, some of which reveal crush artifacts. The smear background contains abundant stripped cytoplasmic particles. Papanicolaou stain, 3200 (A), 3600 (B), and 3400 (C). D: The tumor cells (arrows) contain D-PAS positive cytoplasmic granules. Benign ductal cells (arrow heads) show diffuse cytoplasmic staining. D-PAS stain, 3400. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
plasm ratio and uniform nuclei with a smooth contour and finely clumped chromatin. The nuclei had one or two prominent nucleoli and the cytoplasm was dense and granular. Approximately, 50% of the tumor cells contained numbers of round or fusiform coarse granules that were positive for diastase-digested periodic acid-Schiff reaction (D-PAS) (Fig. 2D). Histologically, the tumor nests showed a solid or large trabecular pattern comprising a monotonous population of cells arranged in solid sheets or an acinar pattern with a delicate fibrovascular network. The tumor nests had expansively invaded into the parenchyma, disrupting the wall of the main pancreatic duct, and expanding to fill the branch ducts (Fig. 3A). Microscopic venous invasion was also
Diagnostic Cytopathology DOI 10.1002/dc
CYTOLOGY OF INTRADUCTAL ACC OF THE PANCREAS
Fig. 3. A: The tumor expand to fill the branch ducts. Non-tumorous epithelial cells are seen covering the ductal lumen. Hematoxylin-eosion stain, 3200. B: The tumor cells contain D-PAS-positive granules in their cytoplasm. D-PAS stain, 3400. C: Immunohistochemically, the tumor cells are positive for trypsin. 3400. D: Electron microscopy shows the tumor cells contain round zymogen granules and filamentous inclusions in their cytoplasm. 320,000. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
noted, but no invasion to lymphatic vessels or metastasis to peripancreatic lymph nodes was evident. The cytoplasm contained D-PAS-positive granules in the apical region (Fig. 3B). Immunohistochemically, the tumor cells showed extensive expression of trypsin, a known acinar cell marker (Fig. 3C), and a1-antitrypsin. Scattered individual tumor cells were positive for synaptophysin and chromogranin. Overall, the tumor cells were negative for amylase, insulin, glucagon, somatostatin, CEA, CA19–9, CD10, and CD56. Nuclear expression of p16 and DPC4 was well conserved and nuclear accumulation of p53 and b-catenin was not evident. Ultrastructurally, the tumor cells were less cohesive, having wide intercellular spaces. Desmosomal and tight junctions were scarce. The nuclei were basally oriented and the cytoplasm contained abundant dilated rough endoplasmic reticulum, mitochondria, and two types of large inclusions: round (200–600 nm in diameter) zymogen granules of uniform density and filamentous inclusions (250–800 nm in diameter, up to 3,500 nm long) with fibrillary internal structures (Fig. 3D).
Discussion Accurate diagnosis of pancreatic neoplasm is essential for planning therapies such as surgery, endoscopy, or alternative treatments. Endoscopic brush cytology is one of the most reliable methods for diagnosis of PDCs, which account for the majority of pancreatic neoplasms. They originate in the pancreatic ductal epithelium, generally show infiltrative growth, and often invade and obstruct the large pancreatic ducts. PDCs tend to extend along the
pancreatic ducts, replacing the luminal epithelium, and are often diagnosed by brush cytology.9 In contrast, ACC is usually a solid tumor showing expansive growth, and intraductal growth is quite rare.7–9 Therefore, there is a high probability that pancreatic brush cytology will misdiagnose duct-infiltrative ACC as PDC. In fact, this case was suspected to be PDC on the basis of preoperative imaging. However, its cytomorphological features did not resembled PDC, as the tumor cells had uniform nuclei with a smooth contour, finely clumped chromatin, and dense granular cytoplasm.1,5 In contrast, well differentiated PDC usually shows a “drunken honeycomb” arrangement with an uneven cell distribution, some nuclear overlapping, and variation of nuclear size.1 In poorly differentiated PDC, nuclear pleomorphism and nuclear contour abnormalities are more evident. Furthermore, the tumor cells of PDC contain abundant mucin, often identifiable even by Papanicolaou staining, and their cytoplasm is diffusely D-PAS-positive.1 Cytologically, ACC can mimic pancreatic neuroendocrine tumor (PanNET) and solid-pseudopapillary neoplasm (SPPN).1,2 In fact, these tumor cells commonly have round to oval nuclei and granular cytoplasm, as is the case in ACC.5 However, the nuclei of PanNET usually show a coarsely granular, so-called “salt-and-pepper” chromatin distribution, unlike the tumor cells in this case. Meanwhile, SPPNs commonly show prominent nuclear grooves, hyaline globules with delicate fibrovascular cores and a myxoid stroma. Moreover, the background may be filled with hemorrhagic cyst debris laden with foamy histiocytes and multinucleated giant cells,1,5 which were not observed in this case. Essentially, both PanNET and SPPN are commonly discrete, well circumscribed tumors showing expansive growth. Although they occasionally compress or narrow the large pancreatic duct, blockage of the duct and intraductal extension seem to be rare.9 Intraductal extension is also rare in ACCs, but several reports have indicated that an intraductal variant of ACC exhibits predominantly intraductal polypoid growth in the large pancreatic ducts.7,8 Recently, Ban et al. reviewed the histologic features of 13 case of ACC, of which 7 (54%) showed intraductal polypoid growth of the tumor in the large pancreatic ducts. Among them, four cases showed predominant intraductal tumor growth with a "sausage-like" shape, but the other three cases showed intraductal polypoid growth as well as nodular lesions with expansive invasion, as was seen in this case.9 In both intraductal and nodular lesions, tumor cells proliferated in a solid or acinar pattern with a scant stromal component. Therefore, the pancreatic ducts are an important route of tumor extension, not only for the predominantly intraductal variant but also for conventional ACC, and brush cytology may be a reliable diagnostic method for them. Ultrastructurally, ACCs often contain numerous large cytoplasmic granules, known as zymogen granules, and Diagnostic Cytopathology, Vol. 42, No 4
323
Diagnostic Cytopathology DOI 10.1002/dc
TOYONAGA ET AL.
filamentous inclusions that are thought to lie within the spectrum of zymogen granules.10,11 These inclusions are present in primary pancreatic tumors, particularly pure ACC, but less frequently in mixed acinar-endocrine carcinoma. They have only rarely been identified in PanNET, and have never been reported in SPPN.12,13 Therefore, the presence of these inclusions may serve as an ultrastructural marker of cells showing acinar differentiation. Zymogen granules are known to be PAS-positive and diastase-resistant.3 Certainly not all ACCs have these inclusions, and some tumor cells in this case showed only a sparse distribution of zymogen granules. However, the presence of tumor cells with coarse D-PAS-positive cytoplasmic granules may indicate acinar differentiation.3 Although the common cytoarchitecture of ACC in FNA specimen is small to large, thick, and 3-dimensional clusters with prominent acinar formation, recent studies of FNA reported that abundant stripped nuclei were found at periphery of the loose clusters as our present case.5,6 This discohesive cytoarchitecture, common to both of FNA and brush cytology, may reflect the histological characteristics of ACC; lack of intervening stroma, weak cohesion, and fragility of the tumor cells.14 However, the cytological specimens of our case seemed to be more discohesive than FNA specimens of the previous studies. In addition, some stripped nuclei with crush artifact and abundant cytoplasmic particles observed in our case, that have not noted in the prior studies of FNA specimens, may reflect the artifacts of the brushing during sampling. In summary, we have presented a case of pancreatic ACC with intraductal growth, which was diagnosed by endoscopic brush cytology. It is important to be aware of the characteristics revealed by brush cytology, especially as the incidence of intraductal extension of ACC may be higher than previously considered, and there may be important prognostic and therapeutic implications for the patient. Although a helpful immunohistochemical panel may be necessary in some cases,13–15 a few of the characteristic cytomorphological features described here may be useful for differential diagnosis of ACC from malignant epithelioid neoplasms involving the large pancreatic ducts.
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