Reactive capillary endothelial proliferation (RCEP) is the most common immune-related adverse event (irAE) during Camrelizumab treatment. RCEP occurs in the majority of patients with advanced solid tumors who receive Camrelizumab monotherapy. This irAE mainly occurs in the skin clinically, and RCEP in the breast is quite rare. Here we report a case of a female patient with lung ad-enocarcinoma who developed breast RCEP after Camrelizumab treatment and regressed spontane-ously without drug withdrawal. We analyze the mechanism of its occurrence and its possible clinical significance based on relevant literature, aiming to provide guidance for clinical practice.

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