A 56-year-old man developed epistaxis, hoarseness, and swelling of a finger in March 2010. On the basis of biopsies of the masses in the pharynx and finger, he was diagnosed with extramedullary plasmablastic plasmacytoma, with somewhat immature CD45(+), MPC-1(-), and CD49e(-). CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisolone) and VCAP (vincristine, cyclophosphamide, doxorubicin, and prednisolone) therapy was ineffective, but combination therapy with thalidomide and dexamethasone was highly effective. Thalidomide monotherapy successfully maintained partial remission for approximately 7 months. A mass appeared in the right neck in February 2011, and a biopsy confirmed recurrence. Changes to CD45 negativity and MPC-1 partial positivity were seen, while CD49e negativity persisted, suggesting that the plasmablastic plasmacytoma had reverted to a more immature state. Bortezomib therapy was started in March 2011 and was effective. However, during the second round of treatment, the patient developed acute lung injury, which was improved by steroid pulse therapy. After the discontinuation of bortezomib, the extramedullary mass increased rapidly, and the patient died of multiple organ failure. An autopsy showed that plasmablastic plasmacytomas had infiltrated into multiple organs. Extramedullary plasmacytomas and those that revert to an immature state are associated with a poor prognosis, so further treatment improvements are needed in the future.