TGFB1 and intrahepatic cholangiocarcinoma: TGFB1 can reportedly be synthesized and secreted by tumor cells.[33] We further examined the level of TGFB1 in ICC cell culture supernatants by ELISA and found that cPKM‐WT increased the level of TGFB1 but cPKM‐Δ111–115 did not (Figure 4D).