Inhibiting homologous recombination decreases extrachromosomal amplification but has no effect on intrachromosomal amplification in methotrexate-resistant colon cancer cells.

Gene amplification, which involves the two major topographical structures double minutes (DMs) and homegeneously stained region (HSR), is a common mechanism of treatment resistance in cancer and is initiated by DNA double-strand breaks. NHEJ, one of DSB repair pathways, is involved in gene amplification as we demonstrated previously. However, the involvement of homologous recombination, another DSB repair pathway, in gene amplification remains to be explored.