Cytogenetic analysis was performed on six breast carcinomas. All cases
had 46 as a modal chromosome number and all but one had clonal numeri
cal alterations. The most frequent numerical alterations were the clon
al monosomy of chromosomes 18 and 16, present in four and three of the
six cases, respectively. The only clonal structural alteration found
in one case was del(X)(q24). In one of the cases it was possible to pr
opose the sequence of clonal evolution.