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

Abstract

BACKGROUND: Pancreatoblastoma (PBL) is a rare malignant pancreatic tumor seen predominantly in childhood, and its cytologic diagnosis remains challenging. METHODS: Twelve fine-needle-aspirations from 11 adults were analyzed. RESULTS:In total, 6 men and 5 women (median age, 45 years; age range, 32-60 years) had tumors measuring a median 5.6 cm (range, 2.5-12 cm) 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 39.8 months (range, 0.8-348 months), 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 nuclearto-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%). CONCLUSIONS: 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.

The cytologic and immunohistochemical findings of pancreatic mixed acinar‐endocrine carcinoma

“…Other areas typically contain larger cells arranged in syncytium. In cell block preparation squamoid morules are identifiable and a key to the diagnosis 18,22,23 …”

Adult pancreatoblastoma: Current concepts in pathology

“…The aetiology is unknown. Although most tumours are sporadic[ 11 - 15 ], few adult pancreatoblastomas have been described in the setting of familial adenomatous polyposis (FAP)[ 8 , 9 ]. Rare cases in children have been associated with Beckwith-Wiedemann syndrome[ 16 , 17 ].…”

One size does not fit all for pancreatic cancers: A review on rare histologies and therapeutic approaches

“…In the few series available in English literature (accounting for < 100 patients in total), PBL typically appears as a large tumor (up to 20 cm), which is more frequently localized in the pancreatic head. It usually presents with nonspecific signs and symptoms such as abdominal pain, abdominal mass, jaundice, weight loss, chronic diarrhea and upper gastrointestinal bleeding[ 93 - 96 ]. The prognosis is poor, with an mOS of 5 mo in patients who cannot undergo surgery.…”

“…About 40% of patients are metastatic at diagnosis, with the liver being the most common site of secondary involvement; local infiltration of surrounding tissues is also frequent[ 97 ]. Of note, even if PBL is considered to be a sporadic tumor, there have been reports of its association with familial adenomatous polyposis syndrome[ 93 , 98 ] and Beckwith-Weidemann syndrome[ 99 ].…”