BTN1A1 and breast cancer: As milk secretion is one of the most characteristic features of mammalian species, and TDP-43 (encoded by the TARDBP gene) is involved in breast cancer progression29, we hypothesized that TDP-43 may play an important role in milk secretion, while the other candidate, SRSF9, was excluded for further investigation because of its negatively regulatory roles on milk secretion-related genes (BTN and XOR) (Supplementary Fig. 4A, B).