Hints to the diagnosis of mixed acinar-endocrine carcinoma on pancreatic fine-needle aspiration: avoiding a potential diagnostic pitfall.

BACKGROUND: Mixed acinar-endocrine carcinoma (MAEC) is a rare mixed tumor of the pancreas defined by both acinar and endocrine cell differentiation. CASE: We present 2 cases of MAEC initially diagnosed as pancreatic endocrine neoplasm on fine-needle aspiration. Both patients were male, aged 51 and 75 years, and presented with 16-mm and 6-mm pancreatic masses, respectively. Aspirates showed loose aggregates and dispersed single plasmacytoid cells with moderate nuclear size variation, slightly irregular nuclear contours, fine to coarsely granular chromatin, occasional prominent nucleoli, and scant to moderate finely granular cytoplasm. Rare mitotic figures and pyknotic forms were noted in one of the cases. Endocrine differentiation was confirmed by immunocytochemistry which led to an initial diagnosis of pancreatic endocrine neoplasm. Trypsin and lipase immunocytochemistry were later obtained, confirming a component of acinar cell differentiation. Findings were confirmed on surgical excision. CONCLUSION: Because of their potentially more aggressive clinical course and different therapeutic implications, MAECs are an important consideration in the differential diagnosis of pancreatic neoplasms. Certain cytomorphologic features and immunocytochemical markers of acinar cell differentiation may be helpful in raising the possibility of MAEC on cytology.

Hyperplastic (serrated) polyps of the colorectum: relationship of CpG island methylator phenotype and K-ras mutation to location and histologic subtype.

We investigated the frequency of promoter region CpG island methylation (CIM) of hMLH1, MGMT, MINT1, MINT2, and p16 and K-ras mutations in a total of 79 hyperplastic (serrated) polyps (HPs) from 75 patients and correlated the molecular profiles to polyp location in the colorectum, histologic variation, and other factors. Methylation-specific PCR (MS-PCR) was used to assay CIM status. HPs that showed CIM of one or more or two or more of the genes assayed were classified as CpG island methylator phenotype (CIMP) and CIMP-high (CIMP-H), respectively. PCR restriction fragment length polymorphism was used to assay K-ras codon 12 and 13 mutations. Logistic regression indicated a statistically significant trend for increasing odds for CIMP (P = 0.002) and CIMP-H (P < 0.001) according to proximity to the cecum or distance from the rectum. Conversely, K-ras codon 12 mutation was present in 13 of 40 (32.5%) distally located HPs compared with 2 of 39 (5.1%) proximal HPs (P = 0.006). Histologic subtype distribution varied by proximal and distal locations. Frequency of CIMP in serrated polyps with abnormal proliferation (SPAPs), differed significantly from goblet cell serrated polyps (GCSPs) (24 of 26, 92.3% vs. 6 of 13, 46.2%) (P = 0.003) and microvesicular serrated polyps (MVSPs) (26 of 38, 68.4%) (P = 0.03). Frequency of K-ras mutation in GCSPs (7 of 13, 54%) differed from that of MVSPs (6 of 38, 16%) (P = 0.01) and SPAPs (2 of 26, 8%) (P = 0.003). Location in the colorectum and histologic subtype were major determinants of the molecular profile of HPs. The molecular findings of CIMP and K-ras mutations appear to encompass most if not all HPs; CIMP profiles suggest that SPAP is the most advanced morphologic variant. We postulate that MVSP and GCSP may be precursor lesions that, if proximally located or larger, can progress to SPAP. Frequent K-ras mutations and infrequent CIMP distinguish the distal GCSP variant.