Chromosome abnormalities in bilateral breast carcinomas. Cytogenetic evaluation of the clonal origin of multiple primary tumors.

BACKGROUND: Although acquired somatic mutations presumably are crucial in carcinogenesis, nothing is known about the chromosome aberrations of bilateral breast carcinomas.
METHODS: Eighteen specimens from 16 bilateral carcinomas were analyzed cytogenetically. The banding analysis was supplemented with fluorescence in situ hybridization with painting probes.
RESULTS: In two cases, the finding of the same clonal abnormalities in samples from both breasts indicated that the bilaterality had arisen through a metastatic process. In the remaining cases, the absence of similarities between the two sides indicated an independent origin of the two carcinomas. Also, in multifocal lesions within the same breast, examples were found both of karyotypically related and unrelated clones. Altogether, multiple clones without similarities were detected in nine specimens, sometimes together with other, karyotypically related clones. There was no indication that bilateral carcinomas of the breast are cytogenetically different from unilateral ones. The following chromosomal abnormalities were recurrent: der(1;16)(q10;p10), del(1)(q11-n12), del(1)(q42), and del(3)(p12-n13p14-n21).
CONCLUSIONS: Bilateral breast carcinomas have the same cytogenetic aberrations, including evidence of polyclonality, as unilateral carcinomas. The majority apparently arise independently, but some result from a metastasis from one breast to the other. In this sense, bilateral breast carcinomas are similar to multifocal breast cancer in general, of which bilateral tumors may represent a special case.