Gene amplification in human tumor cells

Some tumor cells contain additional DNA sequences that are microscopically observed as HSR or dm. Dm contain repeated sequences. Homogeneous staining regions and dm may be present in the same cell, and both may vary in size and number. HSR or dm are not the result of culture conditions or in vivo treatment. Confusion of dm with acentric fragments or diplococci should be avoided. HSR may be either C band negative or positive. The amplified sequences of HSR are not necessarily located at the normal chromosome sites of these genes in diploid cells. It is assumed that HSR is transcriptionally active in tumor cells as it is in drug resistant cells. The specific gene products of HSR or dm are unknown. HSR and dm may change the response of the cell to cancer chemotherapeutic drugs.