TGFB1 and cancer: However, inhibition of TGFβ signaling released matrix metalloproteinase-9 by stromal fibroblasts, resulting in cleavage of PD-L1 from the surface of PD-L1-expressing cancer cells and myeloid cells and generation of soluble PD-L1, thus potentially desensitizing to anti-PD-1 treatment [157].