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

alpha IFN has recently been recognized as an adjuvant therapy to surgery in melanoma patients. A major issue is to select patients who will benefit fr om this therapy and to avoid toxicity In those who will not respond. The ai m of this exploratory analysis was to identify the predictive factors of re sponse to alpha IFN. The French cooperative group has recently shown that adjuvant therapy of me lanoma patients with low-dose alpha IFN provides a benefit on disease-free interval (DFI). Using this database, predictors of DFI were investigated us ing Cox models and treatment-covariate interactions were sought. Gender, age, Breslow thickness, and baseline WBC count, given an alpha IFN- WBC interaction, were independent predictors of DFI. Baseline WBC count was the only variable for which there was an interaction with alpha IFN, whate ver the Breslow: patients with low WBC count (<6.8 x 10(9)/liter = median) did not benefit from <alpha>IFN (HR=1.27(95%CI: 0.84-1.91); P = 0.26) where as the DFI of patients with high WBC was prolonged (P = 0.0001) with a haza rd 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 greater than or equal to7.2 x 10(9)/liter. The baseline WBC count wa s correlated to baseline neutrophils but not to Breslow thickness or to tim e since last melanoma surgery. alpha IFN 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 confirme d by other studies, may help to identify patients who are most likely to be nefit from alpha IFN.