Chromosome Changes in Primary Tumors*

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Abstract
Chromosome abnormalities have been observed in most, but not all, primary tumors studied to date in man and animals. The extent of the chromosome abnormalities tends to parallel the stage of progression of the tumor; but at all stages a clonal pattern usually exists, the tumor consisting of one or a few stem-lines of cells with a particular chromosome aberration. This aberration is rarely constant from cases to case. Except for a few neoplasms, such as chronic granulocytic leukemia in man, the stem-line predominating in one tumor is different from that predominating in another tumor of the same type. The clonal nature of the chromosome changes indicates that these visible somatic mutations are important in the development of most tumors, but their inconstancy from case to case makes it difficult to consider them as initiators of the neoplastic state. However, the possibility of initiation of consistent somatic mutations too small to be seen by present methods cannot be ruled out. The chromosome findings do not argue against any specific agent''s being etiologic in any particular tumor, since viruses as well as ionizing radiation and various chemicals have now been shown to damage mammalian chromosomes both in-vivo and in-vitro. However, the fact that tumors induced by RNA (ribo-nucleic acid) viruses show chromosome changes much less frequently than do those induced by DNA (deoxyribonucleic acid) viruses may suggest that these 2 types of carcinogenic agents operate through different mechanisms. Clinically, chromosome studies are as yet of limited diagnostic and prognostic value. More information is needed concerning the chromosome changes in early neoplastic and pre-neoplastic lesions of man before the possible usefulness of such studies can be accurately evaluated.

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