IL-10 expression by primary tumor cells correlates with melanoma progression from radial to vertical growth phase and development of metastatic competence.

Downregulation of the immune system facilitates tumor progression at different stages of cutaneous melanoma. Sentinel nodes, the first lymph nodes on lymphatics draining directly from a primary melanoma, are immune downregulated by tumor-generated immunosuppressive cytokines, including interleukin-10 (IL-10). To better understand the kinetics of sentinel node suppression, we investigated IL-10 expression by melanoma cells and tumor-associated macrophages and lymphocytes at different stages of primary melanoma evolution. We used reverse-transcriptase in situ PCR to identify the cellular sources of IL-10 mRNA in 39 melanomas. IL-10 mRNA was identified in tumor cells of 2 of 6 melanomas in situ (33%), of 17 of 21 invasive melanomas (81%) and of 11 of 12 metastatic melanomas (92%). Higher IL-10 expression correlates with tumor progression, with differences between melanoma in situ, invasive melanoma and metastatic melanoma. In primary melanomas, the IL-10 mRNA content of tumor cells correlates with Clark's level. There was significantly more IL-10 mRNA in vertical growth-phase melanoma cells than in radial growth-phase cells. In a logistic regression model, moderate-to-high IL-10 mRNA expression by tumor cells was significantly associated with vertical growth-phase melanoma. IL-10 mRNA was detected in melanoma-associated macrophages and lymphocytes. In invasive melanomas, IL-10 mRNA reactivity of macrophages decreased as Clark's level increased. Alterations of immunity by IL-10 derived from melanoma cells and melanoma-associated macrophages and lymphocytes potentially facilitate evolution of the primary melanoma and render regional lymph nodes susceptible to metastases.