Pancreatoblastoma: Cytologic and histologic analysis of 12 adultcases reveals helpful criteria in their diagnosis and distinction from common mimics.

Abstract

Pancreatoblastoma (PBL) is a rare malignant pancreatic tumor seen predominantly in childhood, and its cytologic diagnosis remains challenging. Twelve fine-needle-aspirations from 11 adults were analyzed. In total, 6 men and 5 women (median age, 45years; age range, 32-60years) had tumors measuring a median 5.6cm (range, 2.5-12cm) located in the pancreatic head (n=7) or tail (n=4), including 3 with familial adenomatous polyposis (FAP)/FAP-related syndromes and 4 with metastasis at diagnosis. The median follow-up was 39.8months (range, 0.8-348months), and 5 patients died of disease. The original cytology diagnoses were: PBL (n=2), neuroendocrine neoplasm (n=2), poorly differentiated neuroendocrine carcinoma (n=2), well differentiated neuroendocrine tumor (n=1), poorly differentiated carcinoma (n=2), "positive for malignancy" (n=1), acinar cell carcinoma (n=1), and epithelioid neoplasm with endocrine and acinar differentiation versus PBL (n=1). Universal cytopathologic findings included hypercellularity; 3-dimensional clusters; and single, monotonous, blast-like cells that were from 1.5 to 2.0 times the size of red blood cells with high nuclear-to-cytoplasmic ratio, fine chromatin, small, distinct nucleoli, and a resemblance to well differentiated neuroendocrine tumor and poorly differentiated neuroendocrine carcinoma. Branching pseudopapillae (n=7) and grooved nuclei (n=3) raised the differential diagnosis of solid-pseudopapillary neoplasm, but with more atypia. Uncommon features included pleomorphism (n=4) and numerous mitoses (n=1). Squamoid morules were seen on smears (n=5) or cell blocks (n=6) in 70% of patients and were characterized by epithelioid cells with elongated, streaming nuclei, fine chromatin, absent nucleoli, and positive nuclear β-catenin (n=6 of 8). The median Ki-67 index was 21% (range, 2%-70%), and neuroendocrine marker expression was common (100%), but acinar markers were variable (63%). A combination of cytologic findings in PBL, including a predominant population of primitive blast-like cells, subtle squamoid morules, frequent neuroendocrine and variable acinar phenotype, should facilitate accurate cytologic diagnosis and distinction from common mimics.