Increased Incidence of Extramedullary Plasmacytomas In Patients with Multiple Myeloma In the Era of Novel Therapy and Effect of Pomalidomide on Extramedullary Disease
Authors: Short Kristen Detweiler , Rajkumar S. Vincent , Buadi Francis , Larson Dirk , Hayman Suzanne R. , Dispenzieri Angela , Gertz Morie Abraham A , Kumar Shaji , Mikhael Joseph R. , Roy Vivek , Kyle Robert , Lacy Martha 
Published: October 2019

Abstract
Abstract 3047

Background:
There is concern about the increased incidence of extramedullary plasmacytomas among patients with multiple myeloma (MM) in recent years (Varettoni et al Annals of Oncology 21: 325–330, 2010). There is controversy about whether novel agents increase the risk of extramedullary disease (EMD). EMD may be associated with decreased overall survival in MM. The purpose of this study was to determine the incidence of true, treatment-emergent EMD in MM among a cohort of patients who have been previously exposed to novel agent (thalidomide, lenalidomide, or bortezomib) therapy, and to evaluate the activity of pomalidomide in patients with EMD.

Methods:
We examined 174 consecutive patients with relapsed refractory multiple myeloma that were enrolled on a phase II clinical trial of pomalidomide plus low-dose dexamethasone. The study cohort was chosen since all patients had previously been exposed to novel agents, and were followed systematically. We adopted a strict definition of EMD which required that in order to be considered extramedullary, plasmacytomas must not have risen from any bone. Thus, masses arising from the bone with a soft tissue component were not considered extramedullary.

Results:
Of 174 patients studied, 16 patients (9.2%) had EMD prior to enrollment. In 3 of the 16 patients, EMD was present at time of diagnosis and was therefore not considered as treatment-emergent disease for this analysis. In 13 of 174 patients (7.5%) EMD developed during the course of MM, after starting therapy. All 13 patients by inclusion criteria were exposed to novel agents prior to the onset of EMD, including 100% to immunomodulatory agents (thalidomide or lenalidomide); and 78% (10 patients) were exposed to bortezomib prior to developing EMD. The median number of lines of prior therapy in these patients was 6, range 1–12). EMD occurred a median of 48 months following diagnosis (range, 16–183 months); the rate of EMD in the first 3 years following diagnosis of MM was 3%. Since all patients had prior exposure to immunomodulatory agents in this cohort, we were able to calculate the median length of time from initiation of immunomodulatory agents to onset of EMD as 24 months (range 7–119 months). The EMD sites involved included the temporal area soft tissue (3), muscle (3 [1 pt with 10 different areas of involvement, 1 pt with 5 muscles involved]), chest wall not attached to bone (3), abdominal/pelvic masses (3), kidney (2), scrotum (2), sinus (1), paraspinal (1), hilar/pleural based (1), paraesophageal (1), subcutaneous tissue (1), pancreas (1), spleen (1), mediastinum (1), pleural fluid (1), liver (1). Per protocol, all patients received pomalidomide (2-4 mg per day) and low dose dexamethasone (40 mg once a week). Of the 13 patients, there were 2 CR (with complete disappearance of EMD), 2 PR, 2 stable disease, 3 with progressive disease, and 4 patients who did not have their EMD re-evaluated. Thirty percent (n=4) of patients had a 50% or greater reduction in size of the EMD including one patient who received concomitant radiation. Overall survival from measured from trial entry was significantly shorter for patients who presented with EMD compared to those who did not have EMD, median 16 months versus not reached, p=0.002 (log-rank).

Conclusion:
We found that 7.5% of patients with relapsed refractory myeloma in the era of novel agents develop EMD during the course of their myeloma, including 3% within 3 years of diagnosis. The underlying reasons for the possible increased incidence of EMD may include better radiographic detection (the role of PET/CT scans and MRI), improved overall survival of patients in recent years, and the possibility that novel agents may increase the risk for strictly defined, true EMD among patients who did not have EMD at time of initial MM diagnosis. These need further study.

Disclosures:
Dispenzieri: Celgene: Honoraria, Research Funding; Binding Site: Honoraria. Gertz:Celgene: Honoraria; Millennium: Honoraria, Membership on an entity's Board of Directors or advisory committees. Kumar:Celgene: Consultancy, Research Funding; Millennium: Research Funding; Merck: Consultancy, Research Funding; Novartis: Research Funding; Genzyme: Consultancy, Research Funding; Cephalon: Research Funding.