Response to systemic therapy in patients with metastatic fumarate hydratase (FH) deficient renal cell carcinoma (RCC).

Abstract

686 Background: FH-deficient RCC (FHRCC) is characterized by unique pathologic features and lack of FH staining on immunohistochemistry (IHC). Most cases are associated with germline FH mutations and poor prognosis, but there is limited data on the efficacy of systemic therapy. Methods: Patients with metastatic FHRCC, defined by presence of FH germline or somatic mutation with loss of FH by IHC [FH and 2-succino-cysteine (2SC)], were identified from an institutional database. Clinical and treatment data was obtained from electronic records. The primary outcome was best objective response rate to first, second or third-line systemic therapy by blinded investigator RECIST v1.1 assessment. Results: 32 patients (median age 46; range 20-74; M:F, 20:12) were identified. All patients had evidence of FH-deficiency by IHC, 23 (72%) had germline FH mutations, 9 (28%) had somatic only FH mutations. 20 patients (62.5%) presented with de novo metastatic disease. Most common sites of metastasis were retroperitoneal lymph nodes (82%), lung (78%) and peritoneal spread (70%); no patients developed brain metastases. Median overall survival (OS) from diagnosis of metastatic disease is 28.1 months (95% CI: 14.9, 33.8). Median follow-up is 14.8 months. 25 patients were evaluable for response to first-line therapy, 5 to second-line and 4 to third-line therapy (Table). Most common first-line therapies were combination mTOR/VEGFR (50%) and VEGFR monotherapy (20%). ORR to first, second and third-line therapy was 40%, 20% and 25%, with no complete responses. 8 patients who received IO monotherapy were evaluable; 3 had stable disease, no responses were seen. Conclusions: Patients with FHRCC show distinct patterns of disease progression with primary peritoneal spread. Although there was high ORR to VEGFR/mTOR inhibitor combinations, there were limited responses to IO monotherapy.[Table: see text]