Increased Proportion of the Squamous Cell Carcinoma Components Is Associated with Aggressive Behavior and a Worse Prognosis in Resected Pancreatic Adenosquamous Carcinoma

Purpose Pancreatic adenosquamous carcinoma (PASC) is a subtype of pancreatic cancer with a poorer prognosis than pancreatic ductal carcinoma (PDAC). The pathogenesis of this histological subtype has not been fully explained due to its rarity. Methods Of the 245 patients who underwent pancreatic resection for pancreatic cancer, six (2.3%) were diagnosed with PASC. They were retrospectively allocated to Group A (≥ 50% adenocarcinoma components) or Group S (≥ 50% squamous cell carcinoma components). Results The six patients with PASC were all males between the ages of 63 and 77 years, with tumors of 12 to 52 mm in diameter. Tumors were located in the pancreatic head ( n = 2) and the pancreatic tail ( n = 4). Relative to Group A, all three patients in Group S had larger tumors diameters, ≥ 40 mm with invasion to other organs. Cancer-specific survival of Group S was worse than that of the PDAC group (median survival, 1.5 years vs. 4.1 years). All patients in Group A were alive at the end of follow-up. Recurrence-free survival of Group S was inferior to that of the PDAC group (median survival, 0.2 years vs. 1.8 years; Group A, not defined). Immunohistochemistry revealed the MIB-1 positivity rate in squamous cell carcinoma regions was 1.8 times higher than that in adenocarcinoma regions in the same specimens. Conclusion In PASC patients, an increased proportion of squamous cell carcinoma components was associated with aggressive behavior and a worse prognosis. This was due to the high MIB-1 positivity rate of squamous cell carcinoma components.