Chromosomes in cancer and leukemia.

An important aspect of chromosomes in human cancer is the fact that, with extremely rare exceptions, the chromosomal changes, if present, are confined to the malignant cells. Thus, in the case of cancer of the stomach or bladder, for example, the karyotypic aberrations can only be found in the cancerous cells, whereas the surrounding normal cells or those within the tumor (such as the leukocytes) have a normal chromosomal constitution. In the case of leukemia the chromosomal changes are best observed in the cells of the marrow, though if sufficient leukemic cells are circulating in the blood, the karyotypic changes can sometimes by established on such cells. In any case, in order to ascertain a reliable karyotypic picture in human cancer or leukemia the malignant cells must be examined and the chromosome constitution ascertained either by a direct technique not involving culture conditions or after short-term culture. Long-term culture of leukemic or cancerous cells generally leads to changes in the chromosomal picture either towards diploidy or towards aberrations resulting from in vitro conditions and, in either case, is not representative of the karyotypic picture in the original malignant cells. Since some tumors have a rather low mitotic index (and this applies occasionally to marrows of leukemia), either a repeat examination has to be undertaken or one has to resort to short-term culture.