To date, the molecular biological mechanisms associated with this carcinomatous transformation remain unknown.<h4>Presentation of case</h4>We present here the case of a 61-year-old patient with invasive ductal of no special type (NST) carcinoma originating in a borderline phyllode tumor with mutation in the PIK3CA gene.<h4>Discussion</h4>To the best of our knowledge, this mutation has never been described in this type of association.<h4>Conclusion</h4>Based on these data, we can better understand the ethiopathogenic molecular mechanisms in this type of lesion. Here, PIK3CA is linked to carcinoma.