GNAS mutations (p.R201H, c.602G>A and p.R201C, and c.602C>T) were identified in 17 (31%) of 55 of disseminated mucinous neoplasms and were found in 8 (35%) of 23 low-grade mucinous neoplasms, 7 (37%) of 19 high-grade mucinous adenocarcinomas lacking a signet ring cell component, and 2 (15%) of 13 high-grade mucinous adenocarcinomas with a signet ring cell component.
Our data suggest that mucinous adenocarcinoma is typified by (1) frequent KRAS mutations and a growing list of gene fusions, but rare TP53 mutations, (2) a low mutation burden overall, and (3) a recurrence-free survival similar to stage-matched nonmucinous tumors, with recurrences limited to the lungs.
86% of GNAS-mutated non-mucinous adenocarcinomas (6/7) were positive for TTF-1 immunohistochemistry, while only 25% of GNAS-mutated IMAs (1/4) were positive for TTF-1.
Therefore, we reviewed clinico-pathological features of thymic mucinous adenocarcinoma in details and analyzed KRAS gene mutations of the present case.
KRAS mutations with synchronous TP53 mutations occur predominantly in low-grade mucinous carcinomas, suggesting a specific molecular background of this ovarian cancer type.
KRAS mutations are characteristic for mucinous LMP tumors and mucinous carcinomas (40-50% of cases) and are also found in a third of serous LMP tumors.
Activating GNAS mutations were found in 8 of the 19 lobular endocervical glandular hyperplasias (LEGH; 42%) and 4 of the 79 endocervical-type mucinous adenocarcinomas (5%) but were never seen in the normal endocervical tissue, minimal deviation adenocarcinomas, endometrioid adenocarcinomas, or squamous cell carcinomas.
KRAS mutations were common (76% of invasive mucinous adenocarcinomas, 68% of mixed mucinous/nonmucinous), and 38% of KRAS mutations occurred with other mutations, especially STK11.
Somatic p53 mutations were detected in only one tumor of the cystadenoma/adenofibroma series (4.2%), in contrast to 38.5% of the carcinomas, among them 57.1% of serous papillary carcinomas, and 12.5 to 22.2% of endometrioid and mucinous carcinomas.
Hierarchical clustering isolated three relevant clusters: (i) cluster of microsatellite stable mucinous adenocarcinomas (54%) with KRAS mutation, and frequent MGMT changes, more frequently located in the left colon, often associated with contiguous precursor adenoma; (ii) cluster of BRAF-mutated mucinous adenocarcinomas (28%) with either microsatellite instability-high or microsatellite stable status, occurring in elderly female patients, nearly all located in the right colon, having the signature of serrated pathway of carcinomas; and (iii) a heterogeneous cluster of microsatellite instability-high mucinous carcinomas (18%), including inherited colorectal carcinomas, displaying a high-grade histological pattern.
The 10 cases of MACA harbored a similar prevalence of TP53 mutations (n=5, 50%) as HAMN but, unlike LAMN and HAMN, some harbored mutations in PIK3CA, APC, FBXW7, PTEN, and SMAD4.
A mutational analysis identified activating GNAS mutations in 16 of 32 low-grade appendiceal mucinous neoplasms (LAMNs) but in none of three mucinous adenocarcinomas (MACs).
Missense mutations in KRAS codon 12 were detected in six of seven (86%) mucinous adenocarcinomas but only 3 of 18 (17%) nonmucinous adenocarcinomas (P = 0.003).
GNAS mutations were detected in two LAMNs and in one MAC, although the GNAS mutation in this MAC was a nonsense mutation (Q227X) expected not to be activating mutation.