NODULAR LESIONS OF MONOCYTIC COMPONENT IN MYELODYSPLASTIC SYNDROME

We report 4 unusual cases of myelodyplastic syndrome with distinct per sistant nodular lesions noted on serial bone marrow examinations, even during remission. The lesions were predominantly composed of immature monocytes that stained positively for CD68. Trisomy 9 and 11 were dem onstrated in the cells of the nodular lesions and surrounding marrow o f 1 patient, indicating the same clonal origin. Evaluation of p53 glyc oprotein, retinoblastoma protein (pRb), proliferation-related protein (Ki-67), multiple drug-resistant enzyme glutathione-S-transferase pi, and topoisomerase IIalpha (Topo IIalpha) revealed decreased topoisomer ase expression within the nodular lesions compared with the surroundin g marrow and absence of Ki-67 antigen within nodular lesions. Most cel ls in the lesion were not in a proliferative cycle, with very low expr ession of Topo IIalpha, which may explain the apparent drug resistance of these nodular lesions.