Thin primary cutaneous malignant melanoma: a prognostic tree for 10-year metastasis is more accurate than American Joint Committee on Cancer staging.
OBJECTIVE
The majority of invasive primary melanomas are thin (< or = 1.00 mm). Since the current staging system imperfectly predicts outcome in patients with such lesions, we sought to develop a more effective classification scheme to better identify both patients at high risk of metastasis who are candidates for further staging and therapy and those with little risk.


METHODS
This prospective cohort study included 884 patients who had thin invasive melanomas. A tree-structured analysis of 10-year metastasis was used to develop a new classification scheme.


RESULTS
The overall 10-year metastasis rate was 6.5% (95% CI, 4.8% to 8.1%). The prognostic tree defined four risk groups: high-risk: men with vertical growth phase (VGP) lesions that had mitotic rates (MRs) greater than 0, and for whom the 10-year metastasis rate was 31% (22% to 42%; n = 90); moderate-risk: women with VGP lesions that had MRs greater than 0 and for whom the rate was 13% (9% to 18%; n = 136); low-risk: patients with VGP lesions that had MR of 0 for whom the rate was 4% (2% to 7%; n = 247); and minimal-risk: patients with invasive lesions without VGP for whom the rate was 0.5% (0% to 1.2%; n = 411). Survival curves differed significantly among the four groups (P <.001).


CONCLUSIONS
Growth phase, mitotic rate, and sex are important prognostic factors for patients with thin melanomas, and they identify subgroups at substantial risk for metastasis. After validation in other populations, the proposed prognostic tree will be useful in the design of clinical trials and clinical management.
Department of Biostatistics and Epidemiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6021, USA. pgimotty@cceb.upenn.edu
Phyllis A
PA
Gimotty
DuPont
D
Guerry
Michael E
ME
Ming
Rosalie
R
Elenitsas
Xiaowei
X
Xu
Brian
B
Czerniecki
Francis
F
Spitz
Lynn
L
Schuchter
David
D
Elder
D000368:Aged; D003663:Decision Trees; D005260:Female; D006801:Humans; D008297:Male; D008545:Melanoma / Q000145:classification / Q000473:pathology*; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis; D009367:Neoplasm Staging / Q000379:methods* / Q000592:standards*; D011379:Prognosis; D011446:Prospective Studies; D012307:Risk Factors; D012878:Skin Neoplasms / Q000145:classification / Q000473:pathology*