CHEK2 and breast cancer: However, these studies focused only on breast cancers from individuals heterozygous for gPVs in CHEK2. The aim of this study was to investigate the molecular profiles of cancers from individuals with biallelic gPVs in CHEK2 (from here on CHEK2-deficient cancers) (11), which may offer explanations why PARPi therapy is ineffective in CHEK2-deficient tumors.