The use of a genotypic marker to demonstrate clonal dominance during the growth and metastasis of a human breast carcinoma in nude mice.

When a mixture of 11 clones of a human breast carcinoma (MDA-MB-435)--each clone transfected with pSV2neo and identified as having a unique insertion site of the gene--was injected into nude mice, the resulting tumors were found to contain only one clone (Neo 24). This clone, identified by the unique restriction fragments on Southern blot analyses, was also found in metastases recovered from the lungs and lymph nodes of the animals. The individual clones showed no differences in in vitro growth, while in vivo the Neo 24 cells produced the largest tumors. Thus, one explanation for the observed clonal dominance in this study could be the more rapid growth in vivo of the Neo 24 cells. This study illustrates how an introduced selectable gene marker can be used in lineage studies of human tumor cell populations.