TK1 and acute promyelocytic leukemia: TK1 is located on the outside of the cellular membrane of colorectal, lung, and breast cancer cell lines [16], and cell lines from hematological malignancies, e.g., Raji cells (Burkitt's lymphoma), HL60 cells (promyelocytic leukemia), and Jurkat cells (acute lymphoblastic leukemia) [27].