Malignant histiocytoses developing in patients with B-cell lymphomas. Report of two cases.

Two patients with indolent B-cell lymphomas (small B-cell and small cleaved cell) developed a coexistent malignant histiocytosis 3 and 6 years after diagnosis of their lymphomas. In both patients, malignant histiocytosis presented as new onset of fever, weight loss, and rapidly progressive bulky disease super-imposed on a previously stable clinical course without constitutional symptoms. Both patients failed to respond to combination chemotherapy. The terminal aggressive phase of indolent B-cell lymphomas usually represents transformation of the original neoplasm to a large non-cleaved or immunoblastic B-cell histology. Malignant histiocytosis has not previously been reported as a second neoplasm in patients with B-cell lymphomas.