The cytogenetic studies of a girl with Fanconi's anemia revealed that chromosome breakage was clearly increased in the peripheral blood lymphocytes, and that in the bone marrow 60 % of the cells had a structural abnormality characterized by a D group chromosome with a larger than normal long arm. It is thought that an in viva rearrangement had taken place in the past and, through clonal evolution, had increased its frequency. A complete review of the literature regarding direct cytogenetic studies of the bone marrow in Fanconi's anemia was performed and concluded that structural rearrangements are not unusual in this disease.

The purpose of this study was to answer two questions: 1. Are patients with potentially leukemic myeloid disorders who develop leukemia necessarily preceded by marrow chromosome abnormalities? and 2. Do all that have such abnormalities develop acute leukemia? Direct bone marrow chromosome studies were performed in 18 patients with pancytopenia and in 10 with several unusual myeloproliferative disorders. The former have been followed between 6 months and 13 years; all had normal karyotypes and no evidence of leukemia. In the miscellaneous group, follow‐up has varied between 6 months and 5 years, six patients had assorted chromosome abnormalities, including two with a clonal evolution. Three have died without evidence of leukemia, one has developed a questionable form of chronic eosinophilic leukemia and two are alive without leukemic transformation. It is concluded that the presence of bone marrow chromosome abnormalities in such patients does not necessarily mean that transformation to acute leukemia is imminent.