Application of Multigene Panel Testing in Patients With High Risk for Hereditary Colorectal Cancer: A Descriptive Report Focused on Genotype-Phenotype Correlation

BACKGROUND: The genetic test solely based on the clinical features of hereditary colorectal cancer has limitations in clinical practice. OBJECTIVE: This study aimed to analyze the results of comprehensive multigene panel tests based on clinical findings. DESIGN: This was a cross-sectional study based on a prospectively compiled database. SETTING: The study was conducted at a tertiary hospital. PATIENTS: A total of 381 patients with high risk for hereditary colorectal cancer syndromes were enrolled between March 2014 and December 2019. MAIN OUTCOME MEASURES: The primary outcome was to describe the mutational spectrum based on genotype-phenotype concordance and discordance. RESULTS: Germline mutations were identified in 89 patients for polyposis hereditary colorectal cancer genes (76 in APC; 4 in PTEN; 4 in STK11; 3 in BMPR1A; 1 in POLE; 1 in POLD1), 89 patients for nonpolyposis hereditary colorectal cancer genes (41 in MLH1; 40 in MSH2; 6 in MSH6; and 2 in PMS2), and 12 patients for other cancer predisposition genes (1 in ATM; 2 in BRCA1; 1 in BRCA2; 1 in BRIP1; 1 in MLH3; 1 in NBN; 1 in PMS1; 1 in PTCH1; 1 in TP53; and 2 in monoallelic MUTYH). If we had used direct sequencing tests of 1 or 2 major genes based on phenotype, 48 (25.3%) of 190 mutations would not have been detected due to technical differences (12.1%), less frequent genotype (4.2%), unclear phenotype (3.7%), and genotype-phenotype discordance (4.7%). The genotype-phenotype discordance is probably linked to compound heterozygote, less distinctive phenotype, and insufficient information for colorectal cancer risk. LIMITATIONS: This study included a small number of patients with insufficient follow-up duration. CONCLUSIONS: A comprehensive multigene panel is expected to identify more genetic mutations than phenotype-based direct sequencing, with special utility for unclear phenotype or genotype-phenotype discordance.