In addition, we have found that loss of SMAD4 promotes lung metastasis of CRC by accumulation of CCR1+ TANs through the CCL15–CCR1 axis, and that CCL15 expression in lung metastases is an independent predictor of a poorer prognosis in CRC patients (Yamamoto et al. unpublished data). Here, CCR1 is linked to colorectal carcinoma.