Possible multiple myeloma dedifferentiation following thalidomide therapy: a report of four cases.

Thalidomide has been shown to be effective in approximately 30% of patients with refractory or advanced multiple myeloma (MM). Here we report on 4 cases of patients treated with thalidomide for refractory MM showing dedifferentiation of the neoplasm. In these cases thalidomide treatment despite reduction of M-component-was followed by disease progression and a very poor clinical outcome which was paralleled by bone marrow plasmacytosis showing marked signs of dedifferentiation, inducing us to speculate on a potential role of thalidomide on dedifferentiation of myeloma cells. In our opinion, a possible dedifferentiation of MM should therefore be taken into account in MM patients treated with thalidomide when clinical course deteriorates despite reduction of M-component.