Clinical correlates of splenic histopathology and splenic karyotype in myelofibrosis with myeloid metaplasia

Splenic extramedullary hematopoiesis is an integral component of myelofibro sis with myeloid metaplasia (MMM) and may be classified into 3 distinct his tologic patterns of infiltration by myeloid precursors: diffuse, nodular, a nd a predominance of immature granulocytes, These 3 histologic patterns occ urred in 121 (56.8%), 75 (35.2%), and 17 (8%), respectively, of 213 patient s with MMM who underwent splenectomy at a single institution. In general, k aryotypic findings in splenic tissue (n = 92) were similar to those seen in the bone marrow. The histologic pattern of immature granulocyte predominan ce, the presence of microscopic splenic infarcts (26 patients), or the dete ction of an abnormal splenic karyotype (52 patients) was significantly asso ciated with decreased postsplenectomy survival. These adverse features were also associated with characteristics of advanced disease. These observatio ns support the bone marrow origin of the myeloid progenitor pool in the spl een of patients with MMM and suggest a prognostic value for splenic histopa thology and karyotype.