Nodular melanoma: a distinct clinical entity and the largest contributor to melanoma deaths in Victoria, Australia

There is a growing body of evidence that nodular melanoma (NM), because of its association with increased growth rate and thickness at diagnosis, accounts for a substantial proportion of melanoma deaths.

We sought to assess the contribution of NM to melanoma deaths in comparison with other tumor subtypes.

Four cohorts were established comprising 5775 cases of invasive primary cutaneous melanoma reported to the Victorian Cancer Registry during 1989, 1994, 1999, and 2004. Original pathology reports were reviewed. Age-standardized melanoma incidence rates were compared from 1989 to 2004 with annual percentage change using Poisson regression.

The incidence of thick tumors (>4 mm) increased by 3.8% (95% confidence interval 1.4 to 6.2) and 2.5% (95% confidence interval -0.5 to 5.5) per year for male and female patients, respectively. The median thickness of NM at diagnosis was 2.6 mm compared with 0.6 mm for superficial spreading melanoma. A third of patients who died from melanoma during the follow-up period had thick tumors (>4 mm), most of which were nodular subtype (61%). NM accounted for 14% of invasive melanomas, but was responsible for 43% of melanoma deaths in a total of 57,461 person-years of follow-up. By comparison, superficial spreading melanoma contributed 56% of invasive melanoma but only 30% of deaths.

Pathology review was limited to reports only. Mortality information relied mostly on death certificate information.

The incidence of thick melanomas continues to increase. Nodular melanoma is clinically distinct and the predominant contributor to melanoma-related deaths, representing a public health challenge in reducing skin cancer mortality.