Efficacy was used to assess for PD and the progression-free survival (PFS) was 317 days.<h4>Conclusion</h4>A phosphatidylinositol-4, 5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) mutation in trastuzumab-treated metastatic HER2-positive breast cancer female had a long PFS by treating with the mammalian target of rapamycin inhibitor in combination with the anti-HER-2 agent inetetamab. The gene discussed is PIK3CA; the disease is breast cancer.