The chromosome constitution of peripheral blood cells and bone marrow cells was studied in a 31‐year‐old man with chronic myelocytic leukemia and his normal identical twin. Evidence for their identity includes similar physical appearance, identical blood group antigens and serum factors, similar fingerprint patterns, and phenylthiocarbamide tasting. A typical Philadelphia chromosome was found in the patient. It was absent in bone marrow metaphases of the nonleukemic twin, 8‐1/2 years after diagnosis of leukemia in the other twin. This supports the view that the Philadelphia chromosome is not inherited. To obtain more information about the concordance rate of monozygotic twins, all affected twin pairs should be reported, and long‐term follow‐up observations are needed.
A 73-year-old man developed malignant reticulosis with secondary sideroachrestic anemia. On eight occasions chromosome analyses were performed which included 208 peripheral blood cells and 403 bone marrow cells. Chromosome number ranged from 40-625. I n marrow a hypopentaploid stemline predominated with a mode at 104-106. Supernumerary chromosomes were found in groups C, D, E, F a n d G, including two markers. Minor diploid, tetraploid and polyploid cell lines were also present. Peripheral blood cells were, with some exceptions, exactly diploid and only 1.5% were near-tetraploid. During progression of the disease more and more hypertetraploid, hypopentaploid a n d polyploid reticulum cells emerged in the bone marrow, suggesting clonal evolution.EIATIONS llLl\Yk.EN CHROMOSOhl.\I. ARER-R rations and deLelopnient of cancer and leukemia have been discussed since the observations of Boveri in 1929.8 Suggesting the theory of somatic mutation, Boveri interpreted the abnormal chromosomal constitution as an essential feature of cancer cells. Others,Tz 10 however, considered these chi omosomal aberrations as only secontlai y phenomena. Recently Yamada et a1.10 pointed out that the escape from diploidy to m e w ploidy is a necessary step for the survilal of the cancer cell. Lejeunelg states that chromosomal aberrations are probably neither the cause nor the effect of cancer but that they represent the neoplastic proce3s itself.T h e orcurierice of polyploid cells in malignant tumors is well known. T h e chromosome number of the majority of solid tumors was in the triploid-hypotetraploid range.23-33940
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