SDHx mutations and temozolomide in malignant pheochromocytoma and paraganglioma

Malignant pheochromocytomas (PHEOs)/paragangliomas (PGLs) are rare tumors for which clinical outcomes remain poorly defined and therapeutic options are limited. Approximately 27% carry pathogenic germline succinate dehydrogenase (SDHx) mutations; the presence of such mutations has been correlated with response to temozolomide (TMZ). We aimed to investigate the association between germline mutations in SDHx and response to TMZ. We retrospectively identified patients with metastatic malignant PHEO/PGLs treated with TMZ- based chemotherapy at Dana-Farber Cancer Institute between 2003 and 2020. The correlation between response by Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 and PET Response Criteria in Solid Tumors (PERCIST) and the presence of SDHx mutations in the germline and tumor was evaluated. Nineteen patients received TMZ. Seventeen underwent germline assessment: 9 (53%) carried a pathogenic SDHx germline mutation. Fifteen patients were evaluable for response by RECIST 1.1: 6 (40%) partial response, 4 (27%) stable disease, and 5 (33%) progressive disease. Overall median progression-free survival was 2.2 years. Three-year overall survival (OS) was 58%. Median PFS was 1.3 years and 5.5 years for carriers and non-carriers, respectively and OS was 1.5 years and not estimable for carriers and non-carriers, respectively. The response by PERCIST criteria in nine patients correlated with the RECIST 1.1 assessment. Our series represents one of the largest analyses of patients with malignant PHEOs/PGLs treated with TMZ who have available germline data. The incidence of pathogenic germline SDHx mutations was similar to what has been previously published, though our analysis suggests that there may be a limited association between response to TMZ and pathogenic germline SDHx mutations.