TIMP1 and nonpapillary renal cell carcinoma: The combination of MMP9 produced by M0 macrophages and IL-4-induced M2 polarization reducing TIMP1 promotes angiogenesis in ccRCC and is a mechanistic explanation of the hallmark angiogenesis gene set being enriched in the M0-high cluster, which is also moderately enriched in M2-macrophages.