CHI3L1 and breast cancer: We therefore assessed CHI3L1 expression in the lungs of mice inoculated with 4T1 mammary tumor cells at 2 weeks post-cell implantation, a time point at which no visible micro-metastasis is observed in the lungs (data not shown), and at 5 weeks when metastasis of 4T1 cells is known to be well-established (Yan et al., 2010; Libreros et al., 2012).