[Characteristics of KRAS and HER-family gene mutations in ampullary cancer]

Objective: To investigate the variations and co-alteration of KRAS and HER-family genes in the patients with ampullary carcinoma. Methods: A total of 37 formalin-fixed paraffin-embedded primary ampullary carcinoma specimens, which were collected at Peking Union Medical College Hospital from April 2019 to October 2024 were analyzed for KRAS and HER-family gene mutations using next-generation sequencing (NGS). Immunohistochemistry (IHC) was performed for HER2 protein expression in HER2 mutation cases and fluorescence in situ hybridization (FISH) for further gene status in HER2 IHC 2+cases. Results: In our cohort (22 males, 15 females; 31-82 years old), KRAS gene mutations were detected in 51.4% (19/37) of cases, with G12D being the most frequent abnormality (7/19), followed by G12V (5/19) and Q61R (3/19). Other variants of KRAS gene included G12C, A146T, N116H, and Q61H (each 1/19). In this cohort, 27.0% (10/37) of cases harbored HER-family gene alterations with most frequently in HER2 (6/10) and HER3 genes (missense mutations mainly). Notably, 3 cases (8.1%, 3/37) with coexistence of KRAS and HER-family genes mutations were recognized in our series, including KRAS p.G12D/HER2 p.V842I/HER2 p.V777L (c.2329 G>T)/HER3 p.Asp581Asn, KRAS p.Q61R/HER4 p.D1018H and KRAS p.G12C/HER2 p.R678Q. Additionally, a mutation of HER3 p.V104L (c.310 G>C) was identified in our population. Moreover, 4 novel mutations including HER3 p.V296E, HER3 p.V920L (c.2758 G>T), HER3 p.Asp581Asn, and HER4 p.D1018H were detected. In 6 tumors with HER2 gene changes (16.2%, 6/37), 5 variants with the high proportion of HER2 p.S310Y (3/6) were revealed. A tumor (HER2 IHC 2+) with HER2 p.S310Y presented HER2 gene amplification confirmed by NGS and FISH, and another one (also HER2 IHC 2+) with HER2 p.L755S possessed HER2 gene amplification determined by FISH assay. Conclusion: In ampullary carcinoma, co-alteration of KRAS and HER-family genes is observed, and HER2 gene mutations account for more than half of HER-family gene abnormities, which may be accompanied by gene amplification.