Incidence and Outcome of Soft-Tissue Plasmacytomas in Patients with Multiple Myeloma before and after the Introduction of Novel Drugs

INTRODUCTION: Plasmacytomas (Ps) are frequent in patients with multiple myeloma (MM) and are considered to be associated with poor prognosis. There are two types of Ps: 1) paraskeletal plasmacytomas (PPs) consisting of soft-tissue masses arising from focal bone lesions and 2) extramedullary plasmacytomas (EMPs) consisting of soft-tissue masses with no contact with bone. However, the outcome of patients who develop Ps at diagnoses or at relapse as well as the outcome of the two types of Ps is not well established.

AIM: To analyze the incidence, characteristics and outcome of patients with MM and Ps treated at our institution between 1970-2014 as well as the outcome of these patients before (period 1: 1970-1999) and after (period 2: 2000-2014) the introduction of novel drugs.

PATIENTS: A total of 1.116 multiple myeloma patients (548 males, 568 females) were diagnosed and treated at our institution from January 1970 to December 2014.

RESULTS: Overall, 220 patients (19.7%) had Ps at diagnoses (17.1% PPs and 2.6% EMPs). The incidence of PPs in period 1 was 12.9% versus 21.6% in period 2 (p<0.0001) while the incidence of EMPs remained unchanged over the years (2.5% versus 2.6% in periods 1 and 2, respectively). The median OS of patients with PPs was 3.5 years (2.1 years in period 1 and 5.2 years in period 2) while the median OS of patients with EMPs was 1.8 years (1.3 years in period 1 and 3.9 years in period 2) being the diference in OS statistically significant between patients with PPs and EMPs (p=0.03). The OS of patients without Ps was 3.4 years (2.6 years in period 1 and 4.8 years in period 2) which was similar to the OS of patients with PPs (p=0.5) and significantly longer than that observed in patients with EMPs (p=0.03). The overall incidence of Ps at relapse was 21.6% (15% PPs and 6.6% EMPs). 43% of patients with Ps at diagnoses developed Ps at first or subsequent relapses versus 14.6% of patients without Ps at diagnoses (p<0.0001). The OS from the time of relapse with Ps was significantly longer in those who relapsed with PPs compared with patients who developed EMPs (median 11.4 versus 10.4 months, p=0.03). Thus, in period 1 the OS for patients relapsing with PPs or EMPs was 7.5 and 8.7 months, respectively (p=0.1) while in period 2 the OS was 20.8 and 14.5 months for patients relapsing with PPs and EMPs, respectively (p=0.08)

CONCLUSIONS: EMPs are more frequent at relapse that at diagnoses (2.6% versus 6.6%) while the incidence of PPs is similar at diagnosis and at relapse (17.1% versus 15%). The development of Ps at relapse is significantly higher in patients who had Ps at diagnoses (43% versus 14.6%). Patients with PPs at diagnosis had similar survival than those without Ps while patients with EMPs had poorer outcome than those with PPs or patients with no soft-tissue involvement, both at diagnosis and at relapse.