Undifferentiated Carcinoma of the Pancreas With Osteoclast-Like Giant Cells Localized in the Main Pancreatic Duct Without Extraductal Invasion: A Case Report and Literature Review

Undifferentiated carcinoma with osteoclast-like giant cells (UC-OGC) is a rare pancreatic tumor and typically presents as a giant hypervascular tumor with rapid growth and intratumoral hemorrhage. UC-OGC localized in the main pancreatic duct (MPD) without extraductal invasion is extremely rare and difficult to diagnose preoperatively. Although the tumor rapidly increases in size and often becomes too large for resection, patients with UC-OGC who undergo curative resection show a better prognosis than those with other types of undifferentiated carcinomas and pancreatic ductal adenocarcinoma (PDAC). We must recognize that UC-OGC could present as an MPD-localized tumor and, therefore, should not miss the chance for resection. In this study, we present an unusual case of UC-OGC that was completely localized in the MPD without extraductal invasion. A 77-year-old Japanese man presented to our hospital with excessive thirst. Blood tests showed elevated glycosylated hemoglobin levels (11.9%). Carcinoembryonic antigen, carbohydrate antigen 19-9, Duke pancreatic monoclonal antigen type 2, Span-1, and neuron-specific enolase levels were within normal ranges. Contrast-enhanced computed tomography (CT) showed a 22-mm indistinct nodule with prolonged enhancement in the pancreatic body and dilatation of the distal MPD. Fluorine-18-fluorodeoxyglucose positron-emission tomography with CT showed uptake at the nodule but no evidence of metastasis. Endoscopic ultrasonography showed that the tumor was a heterogeneous hypoechoic nodule localized in the MPD. Pancreatic juice cytology indicated atypical cells but no evidence of malignancy. We suspected PDAC, acinar cell carcinoma, or an intraductal tubulopapillary neoplasm. We performed laparoscopic distal pancreatectomy and splenectomy, along with lymph node dissection. Histopathological examination revealed a 30-mm intraductal tumor with intratumoral hemorrhage, fibrosis, and angiogenesis. The tumor was composed of atypical spindle cells that were partly positive for cytokeratin AE1/3, CAM5.2, and vimentin and scattered osteoclast-like multinucleated giant cells that were positive for CD68. The tumor was completely localized to the MPD without extraductal invasion or lymph node metastasis. The patient received tegafur, gimeracil, and oteracil potassium as postoperative adjuvant chemotherapy for six months and has been recurrence-free for more than five years. UC-OGC demonstrates rapid growth; however, a good prognosis can be expected with curative resection.