[Macronucleolar transformation of a leukemic lymphosarcoma. Clinical morphologic and molecular biologic parameters].

In a case with leukemic lymphosarcomatosis huge nucleoli developed at a final stage refractory to chemotherapy. The lymphosarcoma cells were characterized before and after their macronucleolar transformation by cell fractionation and by biochemical characterization of their nuclear 45S RNA fraction after high specific labelling with 32P-orthophosphate. The analyses provided evidence for a marked increase in nucleolar 45S RNA production. Processing of preribosomal RNA did not seem to be blocked. The biochemical alterations are discussed especially with respect to a possible significance of biological changes during the development of drug resistance against cytostatic agents.