M1 and M2: there is no "good" and "bad"-How macrophages promote malignancy-associated features in tumorigenesis.

We recently identified tumor-associated macrophages from pancreatic ductal adenocarcinoma sharing pro- and anti-inflammatory characteristics. Already in residence in the setting of chronic pancreatitis, local macrophages confer malignancy-associated features to premalignant pancreatic ductal epithelial cells by both promoting and inhibiting inflammation, either of which can foster malignant conversion. Our findings support the concept that contrasting modes of inflammation can promote tumorigenesis.