Serous Neoplasms of the Pancreas: A Clinicopathologic Analysis of 193 Cases and Literature Review With New Insights on Macrocystic and Solid Variants and Critical Reappraisal of So-called "Serous Cystadenocarcinoma".

Abstract

The literature on "variants" and "malignant" counterparts of pancreatic serous cystic neoplasms (SCNs) is highly conflicted. Clinicopathologic characteristics of 193 SCNs were investigated, along with a critical literature review. For the macrocystic (oligocystic) variant, in this largest series, a demographic profile in contrast to current literature was elucidated, with 21% frequency, predominance in female individuals (4:1), body/tail location (1.7×), younger age of patients (mean age, 50 y), and frequent radiologic misdiagnosis as other megacystic neoplasms. Solid SCNs were rare (n=4, 2%) and often misinterpreted radiologically as neuroendocrine tumors. Available fine-needle aspiration in 11 cases was diagnostic in only 1. Radiologic impression was "malignancy" in 5%. Associated secondary tumors were detected in 13% of resections, mostly neuroendocrine. Secondary "infiltration" (direct adhesion/penetration) of spleen, stomach, colon, and/or adjacent nodes was seen in 6 (3%) fairly large SCNs (mean, 11 cm) with no distant metastasis. Three SCNs recurred locally, but completeness of original resection could not be verified. Our only hepatic SCN lacked a concurrent pancreatic tumor. Literature appraisal revealed that there are virtually no deaths that are directly attributable to dissemination/malignant behavior of SCNs, and most cases reported as "malignant" in fact would no longer fulfill the more recent World Health Organization criteria but instead would represent either (1) local adhesion/persistence of tumor, (2) cases with no histologic verification of malignancy, or (3) liver SCNs with benevolent behavior (likely representing multifocality, rather than true metastasis, especially considering there was no fatality related to this and no reported metastases to other remote sites). In conclusion, in contrast to the literature, the clinicopathologic characteristics of solid and macrocystic SCN variants are similar to their microcystic counterpart, although their radiologic diagnosis is challenging. Recurrence/secondary invasion of neighboring organs occurs rarely in larger SCNs but seems innocuous. An SCN should not be classified as "malignant" unless there is clear-cut evidence of histologic malignancy or documented distant metastasis.