(HealthDay News) — Mortality is similar for patients with single primary melanomas (SPMs) and multiple primary melanomas (MPMs), but relative mortality is considerably higher for patients with thicker SPMs versus thicker MPMs, according to a study published online June 19 in JAMA Dermatology.

Noting that patients with a first primary melanoma are at greater risk of being diagnosed with another, Anne Kricker, Ph.D., from the University of Sydney in Australia, and colleagues compared survival in 2,372 patients with SPMs and 1,206 patients with MPMs of any stage.

After a median follow-up of 7.6 years, the researchers found that melanoma thickness was the principal determinant of mortality (hazard ratio, 7.68 for >4 mm). Ulceration, mitoses, and scalp location were also independent predictors of mortality. After adjustment for these factors, mortality was similar for MPM and SPM (hazard ratio for MPM versus SPM, 1.24; P = 0.18). However, relative mortality for thicker lesions was higher for SPM than for MPM (hazard ratio for >4 mm, 13.56 versus 2.93).

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“In summary, we found no strong evidence of a difference in survival between SPM and MPM patients despite the evidence of other researchers and suggestions that MPM may have a less aggressive biology than SPM,” Kricker and colleagues conclude. “However, to our knowledge, we report for the first time a greater increase in the risk of death with increasing tumor thickness for SPM than for MPM.”