Clinical Features and Survival of Multiple Primary Melanoma: A Belgian Single Center Cohort.

Introduction: It remains unclear whether multiple primary melanoma (MPM) patients have a worse survival prognosis compared with single primary melanoma (SPM) patients.

Objectives: To investigate the demographics, histological features, and survival of MPM versus SPM patients.

Methods: Cox regression analyses compared survival between SPM and MPM patients. Furthermore, demographics and histological features of the MPM cohort were compared with the SPM patients retrieved from dermatopathology files between 2000 and 2019.

Results: Out of 3853 melanoma patients, 95 MPM patients were retrieved: 81 with two primary melanomas (85.2%) and 14.8% with three or more. Mean Breslow of the first melanoma was 0.84 mm [minimum (min): 0 mm, maximum (max): 16 mm, standard deviation (SD) 1.77] versus 0.37 mm (second MPM) (min: 0 mm, max: 2.5 mm, SD 0.50) and 0.33 mm (third MPM) (min: 0 mm, max: 0.6 mm, SD 0.22). The mean Breslow for the second MPM was significantly higher for men than women (0.59 mm versus 0.27 mm). First and second melanoma in MPM patients developed on preexisting melanocytic nevi in 13% and 12%, respectively. In contrast with the mean age of primary melanoma in Belgium for women (58.2 years) and men (63.3 years), MPM patients developed their first melanoma earlier, at 44.8 years and 54.6 years, respectively. The mean distribution of anatomical localization of primary and secondary melanoma was highly similar in women, whereas in men a shift towards lower extremities was observed (19% versus 28%). The thicker the primary melanoma was, the sooner the second appeared. Follow-up (2-4/year) versus (1/year) yielded a mean Breslow of 0.29 mm and 0.55 mm, respectively. Cox regression analysis with time-varying covariate revealed a tendency for a worse prognosis in 5-year survival rates, but this was not statistically significant (p = 0.09). Patient phenotypes were not available on the histological reports.

Conclusion: A closer follow-up regimen of MPM versus SPM patients is probably justified.