SLIT2 and neoplasm: The obvious heterogeneity of CAFs and the recent findings on Slit2- and Wnt3a-expressing, tumor-suppressive fibroblasts (74, 77) suggest that: (1) F1 and F2 represent the two extremes of a spectrum of different phenotypes that CAFs can adopt and (2) the polarization of CAFs stays under the control of the tumor (micro)environment.