It is an object of the present invention to find out a
novel gene marker by which a
drug-
resistant cancer cell can be detected and provide a means of efficiently and comprehensively detecting a
drug-
resistant cancer cell using this marker. In the present invention,
gene amplifications or deletions have been analyzed in
cancer cell strains resistant to drugs, which are anticancer drugs having particularly serious side effects and being administered to
cancer patients at a
high frequency (namely, camptothecins, cisplatins, etoposides, adriamycins (ADM), and
cytosine arabinosides), and parent
cancer cell strains. As a result, it was found out that the acquisition of
drug-resistance to an
anticancer drug in a test
cancer cell can be detected by detecting amplification of one or more genes selected from ABC
transporter genes and BCL2 family genes consisting of ABCA3
gene, ABCB6
gene, ABCB8 gene, ABCB10 gene, ABCC4 gene, ABCC9 gene, ABCD3 gene, ABCD4 gene, ABCE1 gene, ABCF2 gene, BCL2L2, BCL2L10, BCL2L1, and BCL2A1 which are
novel gene markers relating to the acquisition of
drug resistance of cancer cells.