Macrophages give Gas(6) to cancer

In this issue of Blood, Loges and colleagues have identified a novel tumor-promoting mechanism, whereby tumors educate tumor-associated macrophages to produce high levels of the mitogen Gas6, leading to tumor growth and metastasis.¹ Surprisingly, this newly identified protumoral activity of tumor-associated macrophages is restricted to the selective induction of cancer cell proliferation, without interfering with cancer cell survival, tumor-associated inflammation, and angiogenesis.