TPCN2 and breast cancer: Knockdown of TPC2 expression in pulmonary artery smooth muscle cells, MNT-1 human melanoma cells, RIL175 murine hepatocellular carcinoma cells, and 4T1 murine breast cancer cells significantly decreased proliferation in vitro [29, 44–46], demonstrating that TPC2 can control both normal and cancerous cell proliferation.