The Prognosis and Natural History of In-Transit Melanoma Metastases at a High-Volume Centre

Patients with in-transit melanoma metastases (ITM) experience a diverse spectrum of clinical presentations and a highly variable disease course. There is no standardized treatment protocol for these patients due to the limited data comparing treatment modalities for ITM. This is the first study to describe the disease trajectory and natural history of a large cohort of patients with ITM. A retrospective study of patients treated for ITM between 2004 and 2018 at the Peter MacCallum Cancer Centre was performed. Clinical and pathological characteristics for primary and in-transit episodes were analyzed for predictors of relapse-free survival (RFS), distant metastasis-free survival (DMFS), and melanoma-specific survival. A total of 109 patients with 303 episodes of ITM were identified: 52 (48%) females, median age 70.1 years (range 35–92). The median RFS for all episodes was 5 months (95% confidence interval [CI] 4.2–5.7). Eighty-seven percent of episodes involving isolated in-transit lesions underwent surgical excision, compared with 17% involving more than five in-transit lesions. A trend was seen between a greater number of lesions and shorter RFS (p = 0.055). The median DMFS was 34.8 months (95% CI 22.8–51.6). Factors associated with shorter DMFS included primary tumor thickness (hazard ratio [HR] 1.08, 95% CI 1.01–1.15; p = 0.026), site of primary tumor (p = 0.008), and BRAF mutation (HR 2.12, 95% CI 1.14–3.94; p = 0.018). Locoregional relapse is common in patients with ITM regardless of treatment modality. Characteristics of the ITM may predict for RFS, while primary tumor characteristics remain important predictors of DMFS.