A Potential Case of Tubulocystic Ductal Carcinoma of the Pancreas.

We present a case of pancreatic ductal carcinoma with a microcystic appearance. A 64-year-old woman was found to have a pancreatic mass during a routine medical checkup. The tumor was well-circumscribed and multicystic; thus, she was followed up for suspected serous cystadenoma. However, the tumor gradually enlarged in the following 2.5 years; subsequently, she underwent a Whipple procedure. Grossly, the cut surface of the tumor was honeycomb-like with small cysts. Histologically, the cysts were ductal structures lined by a relatively bland, cuboidal or columnar epithelium with mildly enlarged nuclei. No intracytoplasmic mucus was observed. The presence of stromal invasion confirmed the diagnosis of ductal carcinoma. KRAS was wild type. Postoperative course was uneventful, with no recurrence to date (followup period: 5.5 years postsurgery). The present case did not meet any known subtypes of pancreatic ductal carcinoma. The tumor resembled a large duct variant, which typically shows a microcystic appearance. However, unlike the present case, the large duct type usually consists of mucus-rich neoplastic cells. A recent study on cholangiocarcinoma proposed a novel tubulocystic subtype characterized by microcystic neoplastic glands and adenofibromatous stroma, which is morphologically similar to the present case. The present case may correspond to a pancreatic counterpart of tubulocystic cholangiocarcinoma.