Recent studies have demonstrated that exogenous FABP4 promotes cell proliferation, migration, and invasiveness in colorectal cancer and breast cancer.46,47 Similar to these findings, we also found that recombinant FABP4 could promote the proliferation and invasion of FLSs in an RA mouse model, which suggested that FABP4 enhanced the aggressive phenotype of FLSs to promote RA development. Here, FABP4 is linked to breast cancer.