A case of multicentric pancreatic mixed acinar-ductal carcinoma diagnosed by a yogurt-like cell clump flowing from the papilla of Vater

Background Histological confirmation is needed when the pancreatic lesions is uncertain for neoplastic or nonneoplastic. Current case with multicentric pancreatic carcinomas showing indefinite clinical images was successfully diagnosed by a biopsy of a novel object expelled from the papilla. Case presentation A 71-year-old male was referred because of elevated serum pancreatic enzymes. Computed tomography revealed an unclear low-density area in the pancreatic body without evidence of tumor and mild dilation of the upstream main pancreatic duct (MPD). Other images, including abdominal ultrasound, endoscopic ultrasound, and magnetic resonance imaging, did not demonstrate cancerous findings. Endoscopic retrograde cholangiopancreatography showed a crab-claw-like obstruction in the MPD. Surprisingly, the component constituting the obstruction was moved by contrast injection and spilled out of the papilla orifice as a yogurt-like white object. Biopsy of this object by histology revealed a cancer cell clump. Pancreatectomy was performed, and pathology of the resected pancreas showed multiple nodular tumors replacing the acini and extending into the MPD. These neoplasms histologically resembled mixed acinar-ductal carcinoma. Conclusion Current report presented a rare tumor with multicentric pancreatic lesions, preoperatively diagnosed by a biopsy of an uncommon substance.


Background
In the diagnosis of solid pancreatic tumors, non-invasive image examinations, including ultrasonography (US), endoscopic ultrasonography (EUS), computed tomography (CT), and magnetic resonance imaging (MRI), are effective [1][2][3], but they have limitations for definitive diagnosis [2]. EUSguided fine needle aspiration (EUS-FNA) is an excellent tool to obtain histological materials, but it is effective only when the target is visible by EUS [4]. Endoscopic retrograde cholangiopancreatography (ERCP) is also a useful diagnostic tool that enables procurement of pathological samples by aspirated or brush cytology and biopsy [5]. These histological samples are usually pancreatic juice, mucin, brushing materials, lavage fluid, and biopsied pancreatic ductal tissues.
We present a rare case of pancreatic poorly differentiated carcinoma that could not be diagnosed by imaging examinations but could be diagnosed by a yogurt-like white substance that spilled out from the papilla of Vater during endoscopic retrograde pancreatography (ERP). The substance demonstrated unique histologic features.

Case presentation
The patient was a 71-year-old male who was referred for an elevated level of serum amylase. He had no symptoms and no previous history or family history. He used to smoke 20-cigarette a day for 40 years but stopped it 10 years before, and drank alcohol occasionally. Laboratory tests demonstrated elevated serum amylase (234 U/L, normal: 37-125 U/L), pancreatic amylase (193 U/L, normal: 21-64 U/L), and cancer antigen (CA) 19-9 (38 U/mL, normal: <37 U/mL). Abdominal US and EUS showed a diffuse low-echoic area around the pancreatic body (Pb) and a mildly enlarged main pancreatic duct (MPD) upstream. This lesion was ill-defined and looked like chronic pancreatitis (Fig. 1a). Enhanced CT revealed an unclear lowdensity area in the Pb (Fig. 1b). MRI also demonstrated a poorly defined area of low-intensity signal in T1-weighted imaging (T1W) and of iso-intensity in T2-weighted imaging (T2W). Diffusion weighted imaging (DWI) showed an attenuated diffusion level around the Pb, and magnetic resonance cholangiopancreatography (MRCP) showed a segmental stricture of the MPD at the Pb with mild dilation upstream. The second lesion, visible at the pancreas tail (Pt), was a well-demarcated, low-density lesion with faint enhancement at its margin by CT (Fig. 1c). This lesion was visualized as low-intensity signal in T1W, as high-intensity signal in T2W, and as high-intensity signal in DWI, but was invisible in MRCP and enhancement was poor in contrast-enhanced MRI. 18 F-fluorodeoxyglucosepositron emission tomography (FDG-PET) revealed no abnormal uptake in these lesions. From these findings, chronic pancreatitis was suspected for the lesion at the Pb and a pancreatic cyst for the lesion at the Pt.
Endoscopic retrograde pancreatography demonstrated a crab-claw-like obstruction in the MPD (Fig. 2a). However, when the contrast was injected in the upstream duct, the substance comprising the obstruction gradually moved toward the pancreas head (Fig. 2b). The substance flowed from the papilla orifice as a yogurt-like white object (Fig. 2c). Biopsy of the white object showed clumps of poorly differentiated carcinoma cells (Fig. 2d). Our preoperative diagnosis was carcinoma of the Pb associated with a suspicious of upstream cyst, and distal pancreatectomy was performed.
In the macroscopic view of the thin-sliced resected specimen, two independent lesions were recognized in the Pb and Pt (Fig. 3a). The loupe image of the hematoxylin and eosin (HE) section revealed multiple clusters of eosinophilic neoplasms replacing the pancreas acini and extending into the MPD (Fig. 3b). Histologically, the tumor formed an acinar or sheetlike structure, composed of cells with eosinophilic cytoplasm and basally aligned, oval-shaped nuclei (Fig. 3c) and solid structure without any acinar or ductal structure in some area (Fig. 3d), and was compatible with the tissue collected during the preoperative ERP. Ki-67 was positive in the both areas ( Fig. 3c, d). These histological findings resembled those of acinar cell carcinoma (ACC), but trypsin, lipase, and Bcl-10 were all negative by immunohistochemistry (Fig. 3c); the source of the antibodies for immunohistochemistry staining is shown in Table 1. Instead, cytokeratin 19 (CK19), cytokeratin 7 (CK7), and MUC 1 were slightly positive especially in the solid area, which indicated differentiation of ductal adenocarcinoma (Fig. 3d). The tumor grew replacing the surrounding normal less-atrophic pancreatic body tissue, but interstitium was almost kept normal, and the findings of pushing-border or infiltration were relatively poor. The maximal size of this tumor was 35 mm.
Histology of another solitary tumor at the Pt was mostly the same as that of the tumor in the Pb (Fig. 3a). It was contained in a component of neuroendocrine tumor arranged in a ribbon-like pattern, with diffuse expression of synaptophysin and chromogranin A, and negative for Ki-67 (<2%) (Figs. 3e). Thus it was considered that the tumor metastasized in the neuroendocrine tumor in the Pt. The size of this tumor was 17 mm.
In addition to the above two lesions, multiple neoplastic cells nests, replacing the acini and creeping into the Fig. 1 a Endoscopic ultrasonography showed a diffuse low-echoic area at the pancreatic body (Pb) and a slightly dilated upstream main pancreatic duct (MPD) (white arrow). b Enhanced computed tomography (CT) demonstrated an ill-defined, low-density area at the Pb (white arrow). c In the pancreatic tale (Pt), CT revealed a well-demarcated, low-density lesion with faint marginal enhancement small duct, were microscopically detected in the proximal section of the specimen (Fig. 3a). Immunostaining of CK19 was positive within the neoplastic cells and progressed through the excretory ducts. These foci were not evident in the preoperative images, by rapid pathological diagnosis, or even in the macroscopic view of the sliced pancreatic specimens.
The overall pathological diagnosis by UICC criteria was mixed acinar-ductal carcinoma, pT2N0M0 pStage IB, with partial endocrine differentiation. Lymphatic permeation was positive, but no venous invasion or lymph nodal metastasis (0/17) were recognized within the resected materials. Neoplastic cells were floating in the pancreatic duct at the cut end, but the cells were not connective with the basal membrane. The patient received adjuvant chemotherapy with S-1 (120 mg/day) for 6 months and was followed up because of his advanced age.
Twenty-two months after the operation, recurrence occurred in the remaining pancreas. Again, excretion of the yogurt-like substance was recognized at the major papilla. Additional pancreaticoduodenectomy was performed, and the resected specimen showed the same but more poorly differentiated neoplasm spreading into the MPD and branch pancreatic ducts, 45 mm in size (Fig. 3f). A small nodule of hepatic metastasis was also found and removed during the operation. The patient again received S-1 as adjuvant chemotherapy, and is still alive until 13 months after the additional surgery with progression of liver metastasis.

Discussion
We report here a case of multiple mixed acinar-ductal carcinoma of the pancreas demonstrating mostly atypical images and partially invisible by imaging, which was difficult to diagnose without obtaining histological evidence. The crucial pathological sample was a yogurt-like cell clump that flowed out of the papilla during ERP. This unique phenomenon helped us diagnose and treat this rare pancreatic tumor. To the best of our knowledge, such an occurrence has not yet been reported.
Although the histology of ACC-like component was quite typical for ACC, excepting the immunohistochemistry, imaging of the current tumor was not typical, as ACC usually forms a huge and exophytic, well-circumscribed, hypovascular mass [22][23][24][25][26]. Toll et al. report a similar case of ACC showing multifocal intraductal extensions and replacements of normal pancreatic parenchyma throughout the entire pancreas [27]. The current case demonstrated the same progression pattern, and it was considered as a reason for the poor tumor definition in the preoperative images.

Conclusion
In summary, we report a rare case of multifocal mixed acinar-ductal carcinoma of the pancreas. The carcinoma showed atypical imaging findings and was diagnosed by pathological examination of a yogurt-like cell clump that flowed out of the papilla during ERP.