Patterns of brain metastases response to immunotherapy with pembrolizumab

Central nervous system (CNS) metastases from lung cancers and melanoma, significantly contribute to morbidity and mortality. Despite advances in local therapies, there is a need for effective systemic treatments. Pembrolizumab, a PD-1 inhibitor, has shown promise for some patients with untreated brain metastases from melanoma and non-small cell lung cancer (NSCLC). This study aims to analyze the response of brain metastasis to pembrolizumab and associate characteristics like size and location with treatment outcome. This retrospective study used imaging data from a phase II trial of pembrolizumab in melanoma or NSCLC patients with untreated brain metastases. MRI evaluations were conducted at 2 month intervals, with each brain metastasis treated as a distinct tumor for response assessment, based on modified RECIST criteria (maximum 5 lesions, 5 mm target lesions). Of 130 individual target metastases (> 5 mm), in 65 patients with NSCLC (90 metastases) and Melanoma (40 metastases), 32 (24.6