TPK1 and cancer: TPK1 expression increased following 24, 48, and 72 h exposure to 1% O2 in an array of cancer cell lines from multiple tissue origins including breast (MCF7, MDA-MB-231), brain (LN 18, U-87 MG), and intestine (Caco-2, HCT 116, HuTu 80) (Figure 1A).