 It has been found that elevated blood serum levels of TK-1 are associated the presence of many types of malignancy, furthermore, TK-1 has been found to be elevated in serum even before clinical symptoms appear.This offers the potential for earlier therapy.Elevations in serum TK-1 have been found to correlate with the return of breast and other forms of cancer TK-1 can be used to detect cancer earlier, determine what stage it is in, and detect recurrence.