T o characterize the nature of the local cytokine response to cancer, we chose to investigate cytokine patterns in biopsy specimens of basal cell carcinoma (BCC). We hypothesized that a distinct pattern of local cytokine production may be characteristic of BCC, a neoplasia of epidermis, in comparison to the pattern of seborrheic keratosis (SK), a benign growth of epidermis. We analyzed cytokine mRNAs in BCC versus SK by performing polymerase chain reaction on mRNA derived from biopsy specimens. The mRNAs encoding cytokines for IL-4, IL-5, IL-10, and granulocyte macrophage colony-stimulating factor were strongly expressed in BCC lesions and weakly expressed in SK lesions. Conversely, IL-2, IFN-gamma, and lymphotoxin mRNAs were strongly expressed in SK lesions and weakly expressed in BCC lesions. The response to malignancy, BCC, was typified by cytokines characteristic of murine TH2 cells. This cytokine pattern favors humoral immunity with concomitant immunosuppression of cell-mediated immune responses. In comparison, the response to the benign growth, SK, was typified by cytokines characteristic of murine TH1 cells that favor cell-mediated immune reactions. The findings of a distinct cytokine pattern in skin cancer provide a framework to develop strategies for immunologic intervention.