Background and Objectives: In-transit melanoma metastases (ITM) present a therapeutic dilemma with numerous therapies employed to treat this heterogenous disease. There is limited data comparing modalities and few studies follow patients beyond the first in-transit episode. This study follows patients over multiple episodes of ITM to characterise the natural history, patterns of care and current treatment models at a single high-volume melanoma unit.
Methods: 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 analysed for trends in clinical practice and prognostic significance in terms of relapse free survival, distant metastasis free survival and melanoma specific survival.
Results: A total of 109 patients with 309 episodes of ITM treated at Peter MacCallum Cancer Centre were identified. The median relapse free survival (RFS) for all episodes was 5 months (95% confidence interval (CI) 4.2-5.8). Ninety-two percent of patients received surgery at least once, in particular 87% of episodes involving an isolated ITM were treated with surgery, compared to 17% of episodes involving more than five ITMs. Factors associated with shorter RFS included non-surgical management (p=0.026), ulceration of the primary melanoma (p=0.036) and greater number of ITM (p=0.003, univariate). The median distant metastases free survival (DMFS) was 34.8 months (CI 22.8-50.6). Factors associated with shorter DMFS included primary tumour thickness (HR 1.08, CI 1.01-1.15, p=0.035), site of primary tumour (p=0.017) and BRAF mutation (HR 2.27, CI 1.24-4.17, p=0.008).
Conclusions: In patients with a limited number of lesions surgery is first line therapy and is associated with longer RFS than non-surgical modalities. ITM characteristics such as number and treatment modality are associated with locoregional disease but not distant metastases. Predictors of distant metastases are related to primary tumour characteristics This study provides the foundation for future prospective studies to establish prognostic factors associated with in-transit disease and serves as a guide to clinical decision making.