We investigated the biologic meaning of tumor-associated macrophages (TAM) in renal cell carcinoma (RCC). The study group comprised of 83 patients with RCC. TAM was isolated by plastic adherence following enzymatic digestion of surgically removed tumor tissues. In some of the patients, monocytes were also isolated from peripheral blood mononuclear cells by plastic adherence. When TAM and monocytes were compared in the same patients, TAM produced interleukin 6 (IL-6), tumor necrosis factor α (TNFα) and interleukin 1β (IL-1β) without lipopolysaccharide (LPS) stimulation, while monocytes hardly produced IL-6, TNFα and IL-1β without LPS stimulation. However, with LPS stimulation, monocytes produced more IL-6, TNFα and IL-1β than TAM. In stage T1 RCC patients, there was a significant positive correlation between TNFα production of TAM and tumor size. In order to investigate the effects of TAM on cancer cells, TAM was co-cultured with A498, K562 and in some cases, with short-term established RCC lines for 96 h. As a result, TAM largely enhanced cell proliferation. These results suggested that TAM may play an important role in certain steps of tumor progression.

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