PIK3CA and breast cancer: Further, our search for co-occurring or mutually exclusive germline truncation/somatic mutations across 12 cancer types revealed a number of important insights in terms of genes and pathways involved including: (1) the association between germline BRCA1/2 germline truncations and frequent TP53 and infrequent PIK3CA somatic mutations confirm breast cancer clinical subtype classification; and (2) ATM as a bona fide (third frequently truncated) susceptibility gene demonstrated by both burden and LOH analyses is the only common gene highly mutated at both germline and somatic levels.