Highlights from the Literature

Population-Based 20-Year Survival Among People Diagnosed with Thin Melanomas in Queensland, Australia. Adele C. Green, Peter Baade, Michael Coory, Joanne F. Aitken, Mark Smithers. J Clin Oncol 2012; 30(13): 1462-7.

As the incidence of melanoma has increased, and our ability to detect early melanomas has improved, the number of thin melanomas diagnosed each year has also grown. While the prognosis for patients with thin melanomas is considered to be excellent, the specific survival rates and determinants have not been well-studied, and the 20-year survival rates for patients with thin melanomas were actually unknown–until now. The purpose of this study was to determine 20-year survival rates for patients diagnosed with melanomas less than or equal to 1 mm, and to determine the main prognostic factors for those patients.

The authors compiled all available clinical and histologic data from the Queensland Cancer Registry for all patients diagnosed with a single thin invasive melanoma from 1982 to 2006, and matched them against national death registration data. Melanoma-specific survival estimates to December 31, 2007, were assessed, and subgroup differences in prognosis were analyzed using multivariate Cox proportional hazard models.

Included in this analysis were 26,736 patients, aged 15 to 89, with thin invasive melanomas less than or equal to 1 mm, out of a cohort of 44,031 patients with invasive melanoma. Overall 5- and 10-year melanoma-specific survival rates to 2007 were 98.7% and 97.4% respectively, while the 15- and 20- year survival rates were 96.7% and 96.0%. Females had better survival than males overall (98.5% vs. 96.5% at 10 years). Survival generally decreased with increasing age, such that melanoma-specific survival at 10 or more years was below 96.1% for patients aged 65 to 89 at the time of diagnosis. Patients with scalp and neck melanomas had lower long term survival than those with melanomas of the trunk and extremities. Level of invasion below the upper papillary dermis, thickness greater than or equal to 0.75 mm, and acral lentiginous and nodular subtypes were also associated with reduced long-term survival. The impact of ulceration or mitoses could not be assessed, as these features were not routinely included in pathology reports at the time of data collection.

This study constitutes the largest series to date, with the longest follow-up, of patients with thin melanoma. Its significance is enhanced by the fact that its data were derived from a population-based prospective melanoma registry, which is probably more representative of survival outcomes than studies from major melanoma centers with a greater proportion of higher risk patients. The authors have succeeded in stratifying patients with thin melanoma into two groups, low-risk and high-risk, on the basis of two major features: tumor thickness (associated with a four times increased risk of death in patients with melanomas >0.75 mm as opposed to <0.25 mm), and age at the time of diagnosis (associated with a three fold risk when comparing patients younger than age 25 vs. those older than age 65). These results are important because they improve our ability to counsel thin melanoma patients about their long-term outlook. While their chance of long-term survival is very high, a small subset of patients will require greater vigilance in their follow-up, since they are at greater risk of dying of their disease. It may be that we will ultimately recommend sentinel lymph node biopsy for patients with thin melanomas exhibiting more aggressive features, although formal clinical trials will be necessary to define their optimal course of management. As the authors themselves point out, these data provide even more solid justification for continuing efforts to improve early melanoma detection through clinical surveillance and public education, and to reduce melanoma mortality by shifting the thickness distribution of these tumors towards systematically thinner lesions.

Désirée Ratner, MD
Columbia University Medical Center