Satram-Maharaj et al. (2014) showed that MAOA expression was increased in breast cancer cell lines and selective MAOA inhibitors altered the growth, migration, and invasion of anchored non-dependent growth of breast cancer cells. Liu et al. (2020) showed that overexpression of tryptophan 2,3-dioxygenase (TDO2) was positively correlated with breast cancer malignancy and tumor grade; the expression of TDO2 was higher in estrogen-negative and triple-negative breast cancers than in other subtypes and was associated with poorer prognoses in patients with breast cancer. Here, TDO2 is linked to breast cancer.