Frequent PIK3CA Mutations in Radial Scars

Radial scars are breast lesions of uncertain pathogenesis that are associated with a 2-fold increased risk of breast cancer compared with that in controls. Activating point mutations in PIK3CA are found in 25% to 30% of invasive breast cancers; however, they have not previously been investigated in radial scars. We sought to evaluate radial scars for known activating point mutations commonly seen in invasive breast cancer. Sixteen surgical cases containing 22 radial scars were identified from pathology archives. Lesional tissue was macrodissected from unstained paraffin sections; genomic DNA was then extracted and screened for a panel of known hotspot mutations using polymerase chain reaction and mass spectroscopy analysis. Of the 22 radial scars, 14 (63.6%) had PIK3CA mutations (10 with H1047R mutations, 2 G1049R mutations, 1 E542K, 1 E545K). The remaining 8 lesions were wild type for all of the screened genes. Of the radial scars without epithelial atypia, 9/16 (56.3%) had PIK3CA mutations; furthermore, 5/6 (83.3%) radial scars with atypia had mutations detected. In this study, the frequency of PIK3CA mutations was notably higher than the 25% to 30% mutation frequency of invasive breast cancer. This finding raises interesting questions as to the role of PIK3CA mutations in breast cancer development. Additional larger studies are indicated to confirm and extend these observations in understanding the pathogenesis of radial scars and their relationship to breast cancer.