White blood cell count: a prognostic factor and possible subset indicator of optimal treatment with low-dose adjuvant interferon in primary melanoma.

AlphaIFN has recently been recognized as an adjuvant therapy to surgery in melanoma patients. A major issue is to select patients who will benefit from this therapy and to avoid toxicity in those who will not respond. The aim of this exploratory analysis was to identify the predictive factors of response to alphaIFN. The French cooperative group has recently shown that adjuvant therapy of melanoma patients with low-dose alphaIFN provides a benefit on disease-free interval (DFI). Using this database, predictors of DFI were investigated using Cox models and treatment-covariate interactions were sought. Gender, age, Breslow thickness, and baseline WBC count, given an alphaIFN-WBC interaction, were independent predictors of DFI. Baseline WBC count was the only variable for which there was an interaction with alphaIFN, whatever the Breslow: patients with low WBC count (<6.8 x 10(9)/liter = median) did not benefit from alphaIFN (HR=1.27 (95%CI: 0.84-1.91); P = 0.26) whereas the DFI of patients with high WBC was prolonged (P = 0.0001) with a hazard ratio of 0.50 (95% confidence interval, 0.35-0.71). The estimated values of WBC count for which IFN was significantly superior to no-treatment were those > or = 7.2 x 10(9)/liter. The baseline WBC count was correlated to baseline neutrophils but not to Breslow thickness or to time since last melanoma surgery. AlphaIFN prolonged DFI in patients with a high WBC count but not in those with a low WBC count. The results of this exploratory analysis, if confirmed by other studies, may help to identify patients who are most likely to benefit from alphaIFN.