• Targeted sequencing analysis found three cases (7%) harboring PIK3CA mutations (18)• PIK3CA mutations in 20% of NECB and other rare mutations in breast cancer (FGFR1, FGFR4, KDR, HRAS) using a PCR/mass spectroscopy or semiconductor-based sequencing strategy (35)• The most frequently mutated genes were GATA3, FOXA1, TBX3, ARID1A (3/18, 17%), and PIK3CA, AKT1, CDH1 (2/18, 11%) (39). Here, ARID1A is linked to breast cancer.