As the Breslow thickness of a primary melanoma grows, so does the likelihood of survival. However, very little was known regarding Breslow thickness’s predictive usefulness in patients with very thick melanomas.

For a study, researchers sought to determine how long patients with ≥4.0 mm Breslow thickness melanomas lived.

A total of 5,595 individuals (4,107 Dutch and 1,488 Australian) with more or less than 4.0 mm thick melanomas identified between 2000 and 2014 were studied. For overall survival (OS) and recurrence-free survival (RFS), standard and spline Cox regressions were created.

The average duration of follow-up was 3.4 years. As the Breslow thickness climbed to 15 mm, the continuous hazard ratios (HRs) for OS and RFS increased continuously, stabilized at 20 mm, and then fell. Using patients with melanomas 4 to less than 10 mm thick as a reference group, the categorical HR for OS increased up to 15- to -<20-mm thickness category and then decreased (HR, 1.46 [95% CI, 1.29-1.66], P<.0001 for 10-<15 mm; HR, 1.97 [95% CI, 1.55-2.51], P<.0001 for 15-<20 mm; and HR, 1.36 [95% CI, 1.07-1.84], P=.045 for ≥20 mm). Similar patterns were seen with the RFS.

In patients with melanomas≥15 mm in thickness, the progressive association between rising Breslow thickness and decreasing survival is gone.