To determine the mechanism by which telomerase-positive cancer cells switch to ALT and to elucidate the mechanism of ALT induction, we induced telomere-specific DNA damage, disrupted the function of the ATRX/DAXX complex and inhibited telomerase activity in telomerase positive cancer cells, which successfully transformed a telomerase-positive cell line into a ALT-positive cell line. Here, ATRX is linked to cancer.