Case Report of Tumour Response to Capivasertib after Exposure to Alpelisib in PIK3CA-Mutated Metastatic Breast Cancer

Sequential targeting of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B pathway in hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer remains poorly described. We report a case of a 67-year-old woman with heavily pre-treated metastatic hormone receptor-positive, HER2-negative, PIK3CA-mutated breast cancer who achieved a meaningful response to fulvestrant plus capivasertib despite prior treatment with fulvestrant plus alpelisib. After progression through multiple lines of therapy, she was started on capivasertib and fulvestrant following stereotactic radiosurgery for intracranial metastasis. Treatment was complicated by a maculopapular rash, which improved with corticosteroids, temporary interruption, and dose reduction. Imaging after 3 months showed a good partial response in the liver, with stable disease in the lungs and bone. This case suggests that capivasertib may retain clinical activity after prior alpelisib exposure in selected patients with PIK3CA-mutated metastatic breast cancer.