A deleted F group chromosome was observed in five patients with myeloproliferative and lymphoproliferative diseases. Three patients had a small F chromosome with both arms deleted, 19p-q-. Each of these patients had a different disease, acute myelomonocytic leukemia (AMML), lymphosarcoma (LSA), and erythroleukemia, respectively. One patient had a hyperplastic marrow and erythroid hyperplasia for a year prior to the development of acute myelogenous leukemia (AML), and had a small F chromosome with del(20)(q12) which is similar to the small F chromosome reported in patients with polycythemia vera. No banding studies were available on one patient with sideroblastic anemia and possible erythroleukemia. These cytogenetic findings lead us to believe that: (1) there is a high incidence of F chromosome abnormalities in cases with abnormal erythropoiesis; (2) erythroid diseases may be predisposed to the small F chromosome abnormality, which is enhanced by treatment, such as irradiation; and (3) the cells with a small F chromosome are rather stable and can gradually replace cytogenetically normal cells without affecting the clinical course of the diseases, and it is the emergence of additional chromosomal abnormalities in these cells which signal a poor prognosis.
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