OBJECTIVETo analyse the incidence, clinical features, prognosis of bone-related extramedullary disease （bEMD） and its relationship with strict EMD (sEMD) in MM patients.

METHODSThe records of 834 consecutive newly diagnosed patients with MM in our hospital between 1993 and 2013 were retrospectively reviewed.

RESULTS①Among 834 patients at diagnosis, 32 cases (3.8%) showed bEMD, and 40 cases (4.8%) showed sEMD. Patients with bEMD at presentation showed significant lower level of lactate dehydrogenase (180.9 U/L vs 299.2 U/L, P=0.034) and higher overall response rate (ORR) (95.7% vs 66.7%, P=0.009) compared with sEMD patients. While the above two parameters were comparable between patients with bEMD and without EMD. ②As to the prognosis of patients without autologous hematopoietic stem cell transplantation (auto-HSCT), the overall survival (OS) of patients with sEMD, bEMD and without EMD was 14.0, 37.5, and 38.0 months, respectively. The time to progression (TTP) of the three groups was 11.5, 27.0, and 22.0 months, respectively. Compared to the patients with sEMD, the outcomes (both OS and TTP) of the other two groups was significantly better (P<0.05). Patients with bEMD at presentation was comparable to the patients without EMD, but the two groups were better than the patients with sEMD. ③The incidence of bEMD during follow-up was 0.5%. The OS of patients with sEMD, bEMD and without EMD during follow-up was 26.0, 17.0, and 40.0 months, respectively. The TTP of the three groups was 13.0, 11.0, and 25.0 months, respectively. The outcomes (both OS and TTP) of patients with bEMD at relapse/progression showed no significant difference as compared with the other two groups (P>0.05).

CONCLUSIONThe clinical features of MM patients with bEMD are different from the patients with sEMD. Outcomes of this population is significantly better than the latter, and is comparable to the patients without EMD. It suggests that bEMD alone has no negative prognostic significance in MM patients.