Uncovering novel pathogenic variants and pathway mutations in triple-negative breast cancer among the endogamous mizo tribe.

Purpose: The incidence of triple-negative breast cancer (TNBC) in India is higher compared to Western populations. The objective of this study is to identify novel and less reported variants in TNBC in Mizoram, a state with a high cancer incidence in India.

Methods: We analysed whole exome sequencing data from triple-negative breast cancer (TNBC) patients in the Mizo population to identify key and novel variants. Moreover, we analysed reported breast cancer-related genes and pathway alterations.

Results: Somatic mutation analysis revealed that TP53 was the most frequently mutated gene and TP53, CACNA1E, IGSF3, RYR1, and FAM155A as significantly mutated driver genes. Based on the ACMG guidelines, we identified a rare pathogenic germline variant of BRCA1 (p.C1697R) in 13% and a likely pathogenic frameshift insertion in RBMX (p.P106Ffs) in 73% of the patients. We also found that the ATM, STK11, and CDKN2A genes were significantly mutated in germline TNBC samples compared to healthy samples. Moreover, we identified novel somatic variants in CHEK2 (p.K182M) and NF1 (p.C245X), and novel germline variants RB1 (p.D111G), CDH1 (p.A10Gfs), CDKN2A (p.V96G), CDKN2A (p.S12Afs*22), MAP3K1 (CAAdelins0), MSH6 (p.L1226_L1230del), and PMS2 (TTCdelins0). Pathway analysis revealed that most somatic mutations were highly associated with PI3K-Akt signalling pathway and MAPK signalling pathways in TNBC.

Conclusions: These findings identified novel variants and key genes contributing to disease development and progression. Further analysis of less studied genes, including RBMX, MRC1, ATM, CTNNB1, and CDKN2A, in TNBC may reveal new potential genes for targeted therapeutic strategies and contribute to clinical advancements in the treatment of TNBC.