Double Minutes in Human Carcinoma Cell Lines, With Special Reference to Breast Tumors2

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Abstract
Small DNA-containing particles called double minutes (dm) were observed in meta phases during a survey of human tumor cell lines. Detection of dm in uncultured malignant effusions, in a series of 14 breast carcinoma cell lines, and in a cervical carcinoma cell line, and a literature survey indicated that dm may be more common among human malignant cells than previously suspected. Some of the human breast carcinoma cell lines showed a high incidence of dm, which permitted a series of cytochemical studies. The dm stained identically with euchromatic regions of human chromosomes. Unlike typical chromosomes, dm contained neither C-bands nor Cd bands indicative of paracentromeric heterochromatin and centromeres, respectively. The dm were observed to cluster at the ends of chromosomes, and individual dm adhered to chromosomes. This clustering behavior allows dm to pass through cell division in the absence of centromeric regions. These results should alert tumor cytogeneticists to the possibility that their material may contain a low incidence of undetected dm.