CYTOGENETIC ANALYSIS OF MULTIFOCAL BREAST CARCINOMAS - DETECTION OF KARYOTYPICALLY UNRELATED CLONES AS WELL AS CLONAL SIMILARITIES BETWEEN TUMOR FOCI

Cytogenetic analysis was performed on short-term cell cultures of two foci (A and B) from each of three multifocal breast carcinomas. In cas e I, four clones (three related and one unrelated) were detected in sa mple A. In sample B, two of the three related clones and the unrelated clone seen in A were found, as was also a third subclone showing a pa ttern of clonal evolution slightly different from that detected in A. In cases II and III, multiple cytogenetically unrelated clones were fo und in A and B, with only one clone being shared by both foci in each case. Our finding of cytogenetic similarities between macroscopically distinct tumour lesions indicates that the multifocality reflects intr amammary tumour spread rather than the synchronous emergence of pathog enetically independent carcinomas within the same breast. On the other hand, the detection of karyotypic heterogeneity in the form of cytoge netically unrelated clones in all foci suggests that human breast carc inoma may be polyclonal. This polyclonality may be part of the explana tion for the cellular heterogeneity commonly seen at the phenotypic le vel in breast cancer.