Abstract
Background/Aim: Pancreatic-type acinar cell carcinoma (ACC) in the stomach is extraordinarily rare. We pathologically examined two cases with multiple primary carcinomas, including gastric tumors. Patients and Methods: Gastric cancer specimens were examined by immunostaining and electron microscopy. Results: Both cases had cancer cells with acinar patterns, resembling pancreatic ACC. The cancer cells in the first case were positive for exocrine markers, including chymotrypsin, lipase and alpha-1 antichymotrypsin (ACT), as well as neuroendocrine markers, including chromogranin A and synaptophysin. The cancer cells in the second case were positive for chymotrypsin and alpha-1 ACT, while being slightly positive for chromogranin A and synaptophysin. Ultrastructurally, cancer cells contained zymogen granules in both cases. The final diagnosis was pancreatic mixed acinar-neuroendocrine carcinoma and pure pancreatic ACC, respectively. Conclusion: We confirmed two cases with gastric pancreatic-type ACC included in multiple primary carcinomas. This type of double cancer has not been reported previously.
- Acinar cell carcinoma
- mixed acinar-neuroendocrine carcinoma
- stomach
- pancreas
- multiple primary carcinomas
Pancreatic acinar cell carcinoma (ACC) arises from acinar cells and is a rare neoplasm, accounting for only 1%-2% of all exocrine tumors of the pancreas (1). In Japan, a 20-year review by the Pancreatic Cancer Registry of the Japan Pancreas Society included only 87 cases of ACC and ACC accounted for 1 in every 119 cases of ductal cell carcinoma (DCC), of a total of 10,336 cases of DCC (2). Pancreatic-type ACC in the stomach is extraordinarily rare. Very few cases of immunohistochemically and/or ultrastructurally confirmed primary pancreatic-type ACC arising in the stomach have been reported in either pure or mixed form. Indeed, in the English literature, 3 cases of pure type ACC (3-5), 2 cases of mixed acinar-neuroendocrine carcinoma (MANEC) (6, 7) (previously called mixed acinar-endocrine carcinoma (MAEC)) and 1 case of unclassified ACC (8) occurring in the stomach have been reported. Multiple primary malignant neoplasms are biologically independent in patients. However, some of them are associated with hereditary disorders (9). To date, there have been no reports on pancreatic-type ACC of the stomach included in multiple primary carcinomas. We examined two cases with multiple primary carcinomas, including gastric tumors, by immunohistochemical analysis and electron microscopy. The combinations of multiple primary malignant neoplasms in both cases of this study can be found in Lynch syndrome (LS) (10). We further examined one case to see if this combination of tumors was associated with LS.
Patients and Methods
Patients. Two cases of gastric cancer were investigated pathologically. The first case had gastric cancer and his past history included urinary tract cancers. The second case had pancreatic cancer and gastric cancer simultaneously. Detailed clinical information was obtained from medical records. Written informed consent to publish was obtained from the patients or the patients' families.
Histochemical and immunohistochemical analysis. All specimens of resected or autopsied stomach tissue were routinely examined by hematoxylin and eosin (H&E) stain. Diastase-resistant periodic acid-Schiff (PAS), Alcian blue and mucicarmine stainings were also performed. An immunohistochemical analysis of the tumor was performed using formalin-fixed paraffin-embedded 4-μm sections. The antibodies used in this study are summarized in Table I.
Ultrastructural examination. For transmission electron microscopic analysis, small blocks of formalin-fixed specimens were deparaffinized in xylene overnight and, then, refixed in 2% glutaraldehyde. After 120 min at 4°C in 1% osmium tetroxide, the sections were embedded in epoxy resin. Ultra-thin sections were cut with an ULTRACUT UCT (Leica Microsystem, Tokyo, Japan), doubly stained with uranyl acetate and lead citrate and, finally, observed with a JEM-1011 electron microscope (JEOL, Tokyo, Japan).
Antibodies employed in the immunohistochemical study and results.
Second screening for LS. Case 1 was given genetic counseling and written informed consent was obtained from the patient before conducting microsatellite instability (MSI) examination and immunohistochemistry (IHC) to detect the loss of DNA mismatch repair (MMR) protein expression. MSI examination was carried out by FALCO Biosystems (Kyoto, Japan). The antibodies for the DNA MMR proteins MLH1, MSH2, MSH6 and PMS2 are summarized in Table I.
Results
Clinical findings. Case 1: A 67-year-old man, presented with black stool. He suffered from urinary bladder cancer in 2001 (re-diagnosed in 2008) and right renal pelvis cancer and urinary bladder cancer in 2007. All urinary tract cancers were diagnosed as non-invasive papillary urothelial carcinoma, low grade. In addition, in 2013, a laterally spreading tumor in the descending colon was resected by endoscopic submucosal dissection, proved to be by pathological diagnosis tubular adenoma. After consulting a physician, an esophago-gastroduodenal endoscopy revealed a 40-mm raised lesion on the greater curvature of the gastric body. Biopsies were not performed because the patient was taking anti-coagulant medication. He was referred and admitted to our Department for surgery. A computed tomography (CT) scan showed no metastatic lesions elsewhere. In April 2014, we performed a distal gastrectomy with D2 lymphadenectomy. No additional lesions, including in the pancreas, were identified at the time of surgery. He did well in the postoperative period. One month after the operation, chemotherapy (S-1; 80 mg/m2 for four weeks with a two-week interval as one cycle) was initiated. The patient was treated with 8 cycles of S-1 monotherapy. At 1 year and 9 months post-surgery the patient was well without any recurrence or metastasis.
Case 2: A 63-year-old man, presented with abdominal pain, constipation and weight loss. In addition, blood analysis showed anemia. Thus, he was referred to another hospital for further examinations. A CT scan showed a 40-mm mass in the body of the pancreas and multiple hepatic tumors (Figure 1A). An esophago-gastroduodenal endoscopy also revealed a type-2 lesion on the posterior wall at the antrum of the stomach (Figure 1B). The result of the biopsy was initially interpreted to indicate a poorly differentiated adenocarcinoma. Thus, the patient was diagnosed with pancreatic cancer with multiple liver metastases and gastric cancer. In August 2013, he was referred and admitted to our Department. Chemotherapy with gemcitabine plus erlotinib for pancreatic cancer was started and four cycles of the chemotherapy were conducted. In January 2014, he died of sepsis due to lower intestinal obstruction and perforation. A postmortem examination was performed.
Imaging and microscopic findings for Case 2. A: Enhanced abdominal computed tomography showed a 4-cm tumor in the pancreatic body (arrow). B: Endoscopic photograph showed a Borrmann type-2 lesion on the posterior wall at the antrum of the stomach. C: The pancreatic tumor represented moderately to poorly differentiated ductal adenocarcinoma (H&E staining at ×100 magnification). D: The gastric tumor showed an acinar structure (H&E staining at ×100 magnification).
Macroscopic features of pathological findings. In Case 1, the resected specimen included an 85×60 mm type-1 tumor with about a 10-mm stalk located at the base of the tumor (Figure 2A). Its surface was relatively smooth and velvety. The cut surface looked lobulated and there was no bleeding lesion or necrosis within the tumor.
In Case 2, the autopsy showed pancreatic cancer with lymph node, liver and peritoneal metastases, as well as gastric cancer with liver metastases. The gastric cancer appeared as a 65×50 mm type-2 tumor.
Microscopic features of pathological findings. The gastric tumors in both cases were composed of small to medium-sized circumscribed nodules and thin fibrous bands, showing two architectures: acinar and solid. Approximately 80% of the tumors demonstrated an acinar pattern (Figure 2B, C and Figure 1D). The cells were moderately atypical, with granular cytoplasm, enlarged round to oval nuclei, finely dispersed chromatin and indistinct nucleoli. These pathological features correspond to pancreatic ACC. No poorly differentiated adenocarcinoma was identified in the gastric tumor of Case 2. The mitotic activity levels were 40 in Case 1 and 15 in Case 2 per 10 high-power fields. Although all the gastric specimens in both cases were examined and the non-tumorous gastric mucosa showed chronic atrophic gastritis with intestinal metaplasia, neither an ectopic pancreas nor pancreatic acinar metaplasia was found in either of the gastric specimens. The tumor of Case 1 invaded the muscularis propria. Two lymph node metastases were confirmed in Case 1. According to the staging system described in the UICC 7th edition (11), the pathological stage of the tumor in Case 1 was pT2N1M0 Stage IIA. The tumor of Case 2 invaded the subserosa. The pancreatic cancer was histologically diagnosed as moderately to poorly differentiated ductal adenocarcinoma (Figure 1C). Histochemical and immunohistochemical analysis. The cancer cells of both cases were negative for d-PAS. They were also negative for Alcian blue and mucicarmine stains, showing that there was no mucus in the cytoplasm of the tumor cells and no ductal cell differentiation. They were focally positive for cytokeratin (CK) 7 but negative for CK20. Results of immunohistochemical analysis are shown in Table I.
Macroscopic and microscopic findings for Case 1. A: The resected specimen included a Borrmann type-1 protruded tumor. B: The tumor showed an acinar structure (Hematoxylin and Eosin (H&E) staining at ×200 magnification). C: The tumor metastasized to regional lymph nodes and showed an acinar structure (H&E staining at ×400 magnification).
Regarding pancreatic exocrine markers in Case 1, the cancer cells were positive for chymotrypsin in the lymph node metastases, partially positive for alpha-1 antichymotrypsin (ACT) in the gastric cancer and focally positive for pancreatic lipase in the gastric cancer and lymph node metastases (Figure 3A, B, C). Regarding general neuroendocrine markers, the cancer cells were partially positive for chromogranin A and synaptophysin; positive cells accounted for approximately 40% of the neoplastic cell population (Figure 3D, E).
Concerning pancreatic exocrine markers in Case 2, the cancer cells were positive for chymotrypsin and alpha-1 ACT (Figure 4A, B). Regarding general neuroendocrine markers, the cancer cells were focally positive for chromogranin A and synaptophysin; positive cells accounted for approximately 5% of the neoplastic cell population (Figure 4C, D).
In both cases, there was no immunoreactivity for specific hormones, including insulin, glucagon, gastrin, somatostatin, pancreatic polypeptide (PPP) and vasoactive intestinal polypeptide (VIP).
Immunohistochemical findings for Case 1. A: The tumor cells in the metastatic lymph nodes were positive for chymotrypsin (immunostaining at ×400 magnification). B: The tumor cells in the primary lesion were partially positive for α-1 antichymotrypsin (ACT) (immunostaining at ×200 magnification). C: The tumor cells in the primary lesion and metastatic lymph nodes were focally positive for pancreatic lipase (immunostaining at ×400 magnification). D: The tumor cells were partially positive for chromogranin A (immunostaining at ×200 magnification). E: The tumor cells were partially positive for synaptophysin (immunostaining at ×200 magnification).
Ultrastructural examination. Ultrastructurally, many secretory granules of the exocrine type with mild-to-moderate electron density (zymogen granules) were clustered in the tumor cells of both cases (Figure 5). The zymogen granules measured 80-1700 nm in Case 1 and 140-960 nm in Case 2, respectively, and varied from cell to cell. The cytoplasm was also rich in rough endoplasmic reticulum and mitochondria. These findings confirmed the acinar cell differentiation of the tumors. In Case 2, small-sized cored granules of the neuroendocrine type were also seen in some tumor cells, measuring 80-170 nm. Both exocrine and neuroendocrine granules were occasionally seen in the same tumor cells (Figure 5B).
Immunohistochemical findings for Case 2. A: The tumor cells were positive for chymotrypsin (immunostaining at ×400 magnification). B: The tumor cells were positive for α-1 ACT (immunostaining at ×200 magnification). C: The tumor cells were focally positive for chromogranin A (immunostaining at ×200 magnification). D: The tumor cells were focally positive for synaptophysin (immunostaining at ×100 magnification).
Based on light-microscopy, as well as immunohistochemical and ultrastructural findings, the final diagnosis of Case 1 was pancreatic-type MANEC. The final diagnosis of Case 2 was pure pancreatic-type ACC.
Second screening for LS. We performed a first screening for LS using the revised Bethesda guidelines (10) and both cases met the criteria. Thus, we performed a second screening on Case 1 for LS, which included MSI analysis and IHC analysis. MSI analysis showed microsatellite stability (MSS). IHC analysis showed positive staining for MLH1, MSH2, MSH6 and PMS2.
Discussion
In this study, we encountered two cases of pancreatic-type ACC of the stomach included in multiple primary carcinomas synchronously or metachronously. These pancreatic-type acinar cell carcinomas of the stomach were confirmed by histologic morphology, immunohistochemical profile and ultrastructure. One was a pure type ACC and the other a MANEC according to the WHO classification (12). Klimstra et al. previously defined this type of pancreatic tumors as mixed acinar-endocrine carcinoma (MAEC) and this term had been used until recently (13). However, changes to the classification of pancreatic neuroendocrine neoplasms have led to replacement of “endocrine” with “neuroendocrine” to parallel the terminology for the remainder of the gastrointestinal tract (14). Since then, MANEC has also been used. MANEC is generally considered to be a variant of ACC and discriminated from pure type ACC based on the population of neuroendocrine cells (i.e. > 30% of the neoplastic population, as defined by their positive response to neuroendocrine markers) (12), although this criteria is admittedly arbitrary. Indeed, Klimstra et al. reported that 42% of pure type ACCs contained scattered endocrine cells (13, 15). In the present study, the tumor of Case 1 showed what appeared to be a uniform cell population by routine H&E staining; however, approximately 40% of the population was found to be neuroendocrine cells through immunohistochemical analysis. The tumor of Case 2 showed scattered neuroendocrine cells throughout the tumor. Klimstra et al. have reported that two different combinations of cells in MANECs have been found: a tumor with separate acinar and neuroendocrine regions identifiable by light microscopy and a tumor with an apparently uniform cell population by light microscopy but with bidirectional differentiation detected immunohistochemically (13). However, they have also reported that in most MANECs, acinar and neuroendocrine components were equally distributed throughout the tumor. Among reported MANECs arising from the stomach, including our case, the case reported by Fukunaga suggested morphologically distinct acinar and neuroendocrine components (6). The two components in the other cases were not distinguished morphologically (7). Some of previously reported ACCs of the pancreas were not examined by immunohistochemical staining for neuroendocrine markers. These cases could be reclassified as MANECs. Among reported ACCs arising from the stomach, one case was not examined by immunohistochemical staining for neuroendocrine markers and the tumor could not be discriminated between pure type ACC and MANEC (8).
Transmission electron microscopic findings. The tumor cells in Case 1 (A) and Case 2 (B) contained secretory granules of the exocrine type with mild to moderate electron density (arrows). Some tumor cells in Case 2 contained both small-sized cored granules of the neuroendocrine type (arrowheads) and exocrine granules.
The reported cases of pancreatic-type ACC arising from the stomach in the English literature are listed in Table II. Three were pure forms of pancreatic-type ACC, two cases were pancreatic-type MANEC and one case was not subclassified. Previous reports have proposed three possibilities for tumorigenesis, origin and pathobiology of primary pancreatic-type ACC arising in the stomach: (i) pancreatic heterotopia (3, 7, 8), (ii) pancreatic acinar metaplasia of the gastric mucosa (4, 5) and (iii) pluripotential stem cells with multiple differentiation capabilities (5-7). Heterotopic pancreas is a relatively uncommon lesion and has been reported to occur at a large number of sites within the abdomen. The most frequent sites of heterotopic pancreas are the duodenum and gastric pyloroantral region. In the gastrointestinal tract, a heterotopic pancreas usually lies in the submucosa. Adenocarcinomas, occurring from an ectopic pancreas, were reported in about 30 cases in the well-documented English literature (16, 17). Most of these tumors were classified as ductal adenocarcinomas. Almost all reported cases showed the existence of pancreatic heterotopia and indicated that the carcinomas arose in the heterotopia (16, 17). On the other hand, among the reported cases of pancreatic-type ACC arising from the stomach, including ours, none of the cases showed the existence of pancreatic heterotopia. Kusafuka et al. explained that among the reported cases of the carcinomas arising in the heterotopia, some reports failed to find an ectopic pancreas near the tumor and that, during tumor progression, the ectopic pancreatic tissue might be destroyed and vanished (7). Indeed, the incidence of an adenocarcinoma arising from the heterotopic pancreas with the coexistence of a heterotopic pancreas is not clear, because, in clinical practice, further examination is not usually performed to distinguish this type of ductal adenocarcinoma from conventional adenocarcinoma arising from the gastric epithelium if the presence of heterotopic pancreatic tissue cannot be verified. However, considering that there was no heterotopic pancreas in the stomach of all cases of gastric ACC, it seems unlikely that this type of tumor derived from an ectopic pancreas. Pancreatic acinar metaplasia of the gastric mucosa is represented by nests, lobules or isolated pancreatic cells in the gastric mucosa (18). The appearance of these cells within the gastric mucosa has been reported to be correlated significantly with chronic and autoimmune gastritis (18, 19). The prevalence rate of pancreatic acinar metaplasia has been reported to be highest in the cardiac region, although it could be found elsewhere in the stomach but at a much lower rate (18, 20). However, among cases listed in Table II, no tumor was located in the cardiac region and the tumors in 4 cases (50%) were located in the pyroloantral region. Ambrosini-Spaltro et al. reported pancreatic-type acinar cell carcinoma of the stomach with concomitant pancreatic acinar cell metaplasia of the adjacent nonneoplastic gastric mucosa (4). However, among the cases listed in Table II, except for the case reported by Ambrosini-Spaltro et al., 4 cases showed no pancreatic acinar metaplasia in any of the specimens and 3 cases did not refer to the presence or absence of pancreatic acinar metaplasia. The 4 reported cases of primary gastric ACC, which include 3 cases of the pure form of ACC and 1 case of unclassified ACC, were entirely or predominantly submucosal. On the other hand, two cases of gastric MANEC and our two cases of MANEC and pure-type ACC, included mucosal components, although the case reported by Kusafuka et al. and our two cases were advanced carcinomas and their original location, whether in the mucosal layer or submucosal layer, could not be detected. Pluripotential stem cells are probably mucosal in location (21). Thus, it is reasonable to hypothesize that gastric MANEC derived from pluripotential stem cells with acinar and neuroendocrine differentiation capabilities. In this study, pure-type ACC in Case 2 included some amphicrine cells, which co-expressed both acinar and neuroendocrine features, as confirmed by electron microscopy. Thus, the cancer cells in Case 2 had the ability to differentiate into both acinar and neuroendocrine features, despite the fact that they were pure-type ACC. In this study, there was neither pancreatic heterotopia nor pancreatic metaplasia confirmed in the gastric specimens in either case. Although there is the possibility that our advanced carcinomas had overgrown an ectopic pancreas or pancreatic acinar metaplasia, it is thought that the tumors in both of our cases derived from pluripotential stem cells.
Pancreatic-type acinar cell carcinoma of the stomach as it appears in the literature.
We considered the possibility that these types of multiple primaries were attributable to some inherited predisposition. LS is an inherited disease caused by a pathological germ-line mutation in one of the mismatch repair genes, characterized by development of colorectal cancer, as well as LS-associated tumors (9). LS-associated tumors include endometrial, stomach, ovarian, pancreas, bladder, ureter and renal pelvis, biliary tract, brain, small bowel and skin tumors. The revised Bethesda guidelines are widely used in the first screening of LS (10). One of these criteria is the presence of synchronous, metachronous colorectal or other LS-associated tumors, regardless of age. As the multiple primaries of both cases met the criteria of the revised Bethesda guidelines, these patients were candidates as having LS. Thus, we performed secondary screening for LS on Case 1 by MSI and IHC analysis. However, both analyses did not show positive results and it was unlikely that Case 1 was affected with LS. Our hospital covers an area in which the population is about 159,000 and is one of three medical centers in the area. Considering the relatively small population, these two rare cases might indicate that the pathogenesis was related to unknown genetic factors, which could be, at least, partially responsible for pancreatic-type ACC of the stomach or the multiple primaries, including gastric ACC.
Klimstra et al. reported that the biological behavior of ACC of the pancreas was aggressive; however, the prognosis was considerably better than that of DCC (15). More recently, Kitagami et al. reported that the 5-year survival rate for resected cases in Japan was 43.9%, with a median survival time (MST) of 41 months. On the other hand, the 5-year survival rate for unresected cases was 0%, with an MST of 3 months (2). Wisnoski et al. also reported that the overall 5-year survival in 17 geographic sites from the U.S. was 42.8% for ACC (MST; 47 months). Patients with unresected ACCs had a 5-year survival rate of 22%. The 5-year survival was 72% for patients with resected ACCs (22). It is speculated that the abovementioned ACCs were not classified as pure type or MANEC. Liu et al. reported that only 30 or so cases of pancreatic MANEC were reported in the English literature. The MST of pancreatic MANEC after surgical resection of the primary tumor from 21 cases analyzed was about 12 months (23). On the other hand, the prognosis of ACC arising from the stomach is unclear due to few reported cases. In addition, there were only 2 reports of therapy other than surgery. Mizuno et al. reported that their case underwent chemotherapy for liver metastasis from gastric ACC by hepatic arterial infusion (gemcitabine, cisplatin and 5-fluorouracil (5-FU)). After three courses, the size of the tumors dramatically decreased (8). Kusafuka et al. reported that their case underwent chemotherapy (S-1 and cisplatin) but the disease condition progressed (7). In the current study, Case 2 died of pancreatic ductal adenocarcinoma. Case 1 was treated with 8 cycles of S-1 monotherapy after the curative operation. At 1 year and 9 months post-surgery the patient was well without any recurrence or metastases. S-1 is an orally administered drug that is comprised of the 5-FU prodrug tegafur and two molecules, gimeracil and oteracil potassium, which increase the blood concentration, alleviate the gastrointestinal toxicity of 5-FU and enhance the anti-tumor activity of 5-FU (24). Clinical studies using S-1 have proven a significant anti-tumor activity in a variety of the malignant tumors, including gastric and pancreas cancer. Recently, several case reports have revealed successful control of pancreatic ACC using S-1 in Japan (25, 26). The precise prognosis and sensitivity to chemotherapy of this type of gastric tumor is still unknown. These cases should be collected globally and analyzed.
In conclusion, we encountered two cases of pancreatic-type ACC of the stomach included in multiple primary carcinomas synchronously or metachronously. Although we did not discover an associated genetic predisposition, there is a possibility that an unknown genetic predisposition might exist. In addition, this study might contribute to improving our understanding of the pathogenesis of this type of gastric tumor. Further studies should be undertaken to determine the pathogenesis, presence or absence of hereditary predisposition, prognosis and treatment strategy, including appropriate chemotherapeutic regimens.
Footnotes
This article is freely accessible online.
- Received March 10, 2016.
- Revision received May 1, 2016.
- Accepted May 4, 2016.
- Copyright© 2016 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved
