PIK3CA Mutations Can Be Acquired during Tumor Progression in Breast Cancer.

Background: Activation of the PI3K pathway by somatic mutations in the PI3KCA oncogene plays an important role in breast cancer. Mutations in PI3KCA have been described in approximately 30 % of breast carcinomas. Dysregulation of the PI3K pathway may have a significant impact on primary or acquired resistance towards endocrine and anti HER2 targeted therapy. The objective of this study was to assess changes in mutations in PI3KCA between the primary tumor and corresponding later metastatic lesions.Material: Formalin-fixed paraffin-embedded tumor blocks were available from 104 paired samples from primary tumors and corresponding distant metastases. In 99 patients paired PI3KCA mutation results were obtained.Methods: HE69(24 Suppl):Abstract nr 6023.