CXCL1 and neoplasm: Furthermore, the levels of both VEGF (and CD31) and CXCL1 (and CD31) angiogenic factors were significantly reduced in the perivascular areas of tumours grown in Col1a1Cre;Atf4Δ/Δ mice compared with Col1a1Cre;Atf4WT/WT mice (Extended Data Fig. 8f–i), which indicates that the ATF4-deficient perivascular CAFs present a defective source of secreted angiogenic factors.