CYTOGENETIC POLYCLONALITY IN TUMORS OF THE BREAST

Cytogenetically unrelated clones are found in half of all carcinomas o f the breast and also in the epithelial fraction of many benign breast tumors. The chromosomal aber rations thus detected are clearly nonran dom and appear to be the same as those often seen in other tumors as s ole karyotypic anomalies. Clonal chromosome abnormalities are not foun d in histologically normal breast tissue. Cytogenetically unrelated cl ones may be found in both primary tumors and secondary lesions, be it within the same breast (multifocal carcinomas), in the contralateral b reast (bilateral carcinomas), or in lymph node or other metastases. Th e aberrations are present in topologically separate tumor domains and may confer on the cells that harbor them different types of cancer-spe cific behavior, such as the ability to metastasize and invade locally. Whereas the available evidence thus strongly indicates that the cells carrying clonal karyotypic aberrations all are part of the neoplastic parenchyma, it is less certain whether cytogenetic polyclonality actu ally signifies a multicellular tumor origin, although we think that th is is the explanation that best accommodates the cytogenetic data. But even if it should eventually be shown that the seemingly unrelated cl ones have some submicroscopic tumorigenic mutation in common, the obse rved karyotypic heterogeneity is remarkable and goes far beyond what o ne has become accustomed to from most other tumor types. To understand how the various clones interact during mammary carcinogenesis will be a major task in future breast cancer research. (C) Elsevier Science I nc., 1997.