BRCA1 and breast cancer: The yield in Lynch genes among breast cancer patients was 0.5% (17/3,315), higher than a published upper estimate of the prevalence of Lynch syndrome among the general population (0.2%).26 In addition, more than a quarter of patients with colon cancer tested positive for genes that are not considered to be classic colorectal cancer genes; BRCA1/2 alone accounted for 9.7% of pathogenic variants identified in individuals with colon cancer.