Clinical benefit of methotrexate plus vinorelbine chemotherapy for desmoid fibromatosis (DF) and correlation of treatment response with MRI

BACKGROUND: Desmoid fibromatosis (DF) is a rare fibroblastic proliferation that was historically treated with surgery. We report (a) outcomes using low‐dose chemotherapy, methotrexate (MTX), and vinorelbine (VNL) for patients with progressing disease (PD) and (b) whether tumor volume (V (tumor)) and T2 signal on magnetic resonance imaging (MRI) are more reflective of treatment response compared with maximum tumor dimension (D (max)) defined by RECIST1.1. METHODS: Patients with biopsy‐proven DF, treated with MTX/VNL from 1997 to 2015 were reviewed. MRI for a subset of patients was independently re‐evaluated for response by RECIST, V (tumor), and quantitative T2 hyperintensity. RESULTS: Among 48 patients treated for a median 19 months MTX/VNL, only nine (19%) had previous surgery. RECIST‐based overall response rate was complete response (CR) 20 (42%) + partial response (PR) 19 (39%), stable disease (SD) 8 (17%), for a clinical benefit rate of 98%. The median progression‐free survival (PFS) was 120 months, (95%CI 84‐155 months). Thirty‐six (75%) patients had not progressed at a median 38 months from treatment completion. Most common grade 1/2 toxicities included nausea (n = 12, 25%) and fatigue (n = 9,19%) with no grade 3/4 toxicities. In 22 patients with serial MRIs, there was a decrease in D (max) mean by 30%, V (tumor) by 76%, and in 19/22 (86%) a decrease in T2 signal intensity. CONCLUSION: Low‐dose MTX/VNL for a defined duration has high efficacy with sustained benefit and minimal toxicity for treating DF. V (tumor) and T2 signal might better predict treatment response than RECIST.