A Decade of Hereditary Cancer Genetic Testing Results in Asian Indian population: Retrospective Study.

Background Hereditary cancers account for approximately 5% to 10% of all malignancies and are more frequently observed in individuals with early-onset disease or a significant family history of cancer. However, large pan-India datasets describing germline variant distributions across multiple cancer types remain limited. Methods We retrospectively analysed 23,070 individuals who underwent germline hereditary cancer testing at MedGenome Labs Ltd., Bangalore, India from 2016 to 2025. Clinical indication based major cancer sub-type groups were breast cancer (N=10486), ovarian cancer (N=3990), colorectal cancer (N=1275), prostate cancer (N=765), endometrial cancer (N=541) and asymptomatic individuals (N=2,775). Germline testing was conducted using clinically validated multigene next-generation sequencing (NGS) panels, with multiplex ligation-dependent probe amplification (MLPA) used for copy number variant detection in a subset of cases. Results The overall diagnostic yield of genetic testing was 23.85%, with the highest yields observed in colorectal (42%) and ovarian cancers (31.6%), followed by endometrial (22.6%), breast (20.2%) and prostate cancer (8.6%) formed the top 5 cancer types. In addition, there is an asymptomatic group where individuals with no symptoms reported but had a positive family history of cancer, where diagnostic rate was 18.9%. Among breast cancer patients diagnosed at [≤]50 years of age, one of the National Comprehensive Cancer Network (NCCN) criteria for hereditary cancer testing, the diagnostic yield was 24.2%. Individuals with a positive family history had a significantly higher diagnostic rate (2.5% to 16%) compared to those without a positive family history across all cancer types. BRCA1 and BRCA2 were the most frequent genes with pathogenic variants in breast and ovarian cancers, while mismatch repair genes (MLH1, MSH2, MSH6) predominated in colorectal and endometrial cancers, and BRCA2 was the most frequently altered gene in prostate cancer. The well-known BRCA1 gene founder frameshift variant (c.68_69delAG; p.Glu23ValfsTer17) was identified in 358 individuals, representing the most frequent pathogenic variant in the cohort. Additional BRCA1 gene recurrent variants observed in the sample set includes a canonical splice-site variant (c.5074+1G>A;N=123), followed by a non-sense mutation (c.3607C>T;p.Arg1203Ter;N=44). A strong concordance between clinical classification and functional annotations was observed when compared with BRCA1 saturation mutagenesis findings. Reanalysis of variants of uncertain significance and undiagnosed cases improved the diagnostic yield by approximately about 5% average across major cancer types. A multivariate regression analysis showed a positive family history significantly contribute to improved diagnosis. Notably, early genetic testing correlated well with significantly contribute to improved diagnosis, suggestive for universal genetic testing over guideline-based testing. In addition, the regression analysis showed a decline in diagnostic yield with increasing age for all five major cancer types analysed, suggesting that the universal criteria for genetic testing is preferable for early detection. Among breast cancer cases with hormone receptor data, the triple-negative and ER+PR-HER2+ cases had a higher diagnostic rate compared to other subtypes of breast cancer. The MLPA-based CNV analysis further validated additional clinically relevant variants in a subset of the cohort. Conclusions To the best of our understanding, this retrospective study showcases the largest comprehensive characterization of the hereditary cancer genetics in India and South Asian region till date, demonstrating a substantial burden of inherited cancer susceptibility and distinct gene-cancer associations across major tumor types. These findings support the implementation of comprehensive multigene testing, periodic variant reinterpretation, and population-adapted hereditary cancer testing strategies to improve hereditary cancer risk assessment and advance precision oncology in underrepresented populations.