Different karyotypic features characterize different clinico-pathologic subgroups of benign lipogenic tumors.

On the basis of the cytogenetic analysis of tumor cells from a total of 50 lipomas, we conclude that 4 main cytogenetic subtypes may be recognized: (1) tumors with normal karyotype (18 cases); (2) tumors with rearrangements of 12q13-14 (18 cases); (3) tumors with ring chromosomes (6 cases); (4) tumors with other clonal changes (8 cases). This karyotypic heterogeneity parallels other disease characteristics in the following manner: all 6 tumors containing ring marker chromosomes were histopathologically classified as atypical lipomas (6 of the 50 tumors were diagnosed as atypical) or (in 2 cases) lipomas with foci of atypia. In only one single solitary lipoma with focal atypia were no ring chromosomes detected in the tumor cells. This contrasts strongly with the findings in typical solitary lipomas, where rings were found in only 2 of 37 tumors, or, if the 3 tumors with focal atypia are excluded, in none of 34. Furthermore, all 7 multiple lipomas were karyotypically normal, whereas among solitary tumors the corresponding proportion was 11 of 43. We conclude that ring marker chromosomes may be a distinguishing cytogenetic feature of atypical lipomas, and that multiple lipomas, in contrast to their solitary counterparts, are karyotypically normal. These findings emphasize that different tumorigenic pathways are likely to be involved in different groups of benign lipogenic neoplasms.