Chromosomal study demonstrating the clonal evolution and metastatic origin of a metachronous colorectal carcinoma.

Detailed cytogenetic studies were performed on 3 samples of a metachronous rectal carcinoma. Two samples were obtained from the primary tumor, and one from a secondary growth which arose 10 months after surgical removal of the primary. All 149 R-banded metaphases analysed were abnormal and most likely derived from the same modified karyotype: 45, XY, -1, -18, +20 der(6) t(1;6) (q21.100;q22.3), i(17q). These data are consistent with our previous findings that the loss of chromosome 18 and of the short arm of chromosome 17 may be the primary chromosomal changes associated with carcinoma of the large bowel. From all the karyotypes observed, a typical clonal evolution could be reconstructed, indicating that the second tumor was indeed metastatic from the first one, based on similar chromosome markers. An identical secondary chromosomal anomaly, i.e. gain of chromosome 8 or X, occurred independently twice in two different cell populations during the evolution of this tumor.