It is intended to develop a therapeutic strategy for specifically targeting cancer cells having the functional suppression of PSS2. The present inventors have found that PSS1 and PSS2 are in a synthetic lethal relationship, and treatment inhibiting PSS1 serves as a promising approach for the treatment of cancer having the functional suppression of PSS2. It has also been revealed that this therapeutic strategy permits efficient treatment based on companion diagnostics because a PSS1 inhibitor can be administered to a subject selected by using the functional suppression of PSS2 as an index.

It is intended to develop a therapeutic strategy for specifically targeting cancer cells having the functional suppression of PSS2. The present inventors have found that PSS1 and PSS2 are in a synthetic lethal relationship, and treatment inhibiting PSS1 serves as a promising approach for the treatment of cancer having the functional suppression of PSS2. It has also been revealed that this therapeutic strategy permits efficient treatment based on companion diagnostics because a PSS1 inhibitor can be administered to a subject selected by using the functional suppression of PSS2 as an index.