PB2119 CLINICAL PRESENTATION AND OUTCOMES OF SOLITARY PLASMACYTOMA IN A LARGE TERTIARY HOSPITAL: A RETROSPECTIVE COHORT STUDY

Abstract

Background:Solitary plasmacytoma is a rare neoplasm of monoclonal plasma cells presenting as either Solitary Bone Plasmacytoma (SBP) or Solitary Extramedullary Plasmacytoma (SEP), without evidence of systemic disease. Standard treatment typically involves radical radiotherapy resulting in prolonged remissions in the majority of cases. However, previous studies have identified a high‐risk group of patients with an increased risk of progression to multiple myeloma. Due to the rarity of this plasma cell dyscrasia, there are few published clinical trials.Aims:To identify risk factors for progression to myeloma, evaluate survival outcomes and determine the incidence of secondary malignancies in a cohort of solitary plasmacytoma patients.MethodsWe retrospectively reviewed case records of adult patients with plasmacytoma treated in a 15‐year period (2002‐2017) at Addenbrookes Hospital, the regional tertiary hospital for the Eastern region of England. Patients with multiple plasmacytomas or meeting the criteria for multiple myeloma at the time of diagnosis were excluded. Clinical, laboratory and radiological features at diagnosis and during the course of treatment were analyzed. Time to progression to myeloma were recorded and survival outcomes analyzed using the Kaplan‐Meier method. The data cut off date was the 1st of July 2018.Results:Thirty‐three (33) cases of solitary plasmacytoma were identified (Table 1): 26 (79%) SBP and 7 (21%) SEP. The mean age at diagnosis was 63 years with a 2:1 male preponderance. The thoracic vertebrae were the commonest sites for SBP while SEP occurred most frequently in skin and soft tissue. Pain and spinal cord compression were the most frequent presenting symptoms. A paraprotein was detectable in 19 (58%) patients at the time of diagnosis, predominantly IgG (68%). The majority of patients received radiotherapy alone (79%) while two patients received wide local excision as the sole modality of treatment. The median total dose of radiation received was 50 gray in 25 fractions (range: 40Gy‐65 Gy). Over a median follow up of 48 months, 13 patients (39%) progressed to multiple myeloma. Median time of progression to myeloma was 22 months but notably, two patients progressed more than 5 years after radiotherapy. There was a trend towards progression for patients with non‐IgG paraprotein and paraproteinemia >10 g/l (relative risk 2.2, 95% CI 0.8‐5.8). From pooled analysis of overall survival, 5‐and 10‐year survival rates were 80% and 57% respectively (Figure 1). The median progression‐free survival was 85 months (Figure 2). Following progression to myeloma, the median survival was 48 months. Over the course of follow up, 5 patients (15%) developed a second malignancy with lung cancer being the most frequent.Summary/Conclusion:Solitary plasmacytoma generally has a good prognosis but progression to multiple myeloma predicts inferior survival. Previous studies have suggested a number of predictive factors for progression but these have not been validated in large prospective studies. In this retrospective cohort, the presence of a significant (>10 g/l) paraprotein and non‐IgG type appeared to increase the likelihood of progression to myeloma but this observation was limited by the relatively small sample size. In the era of novel therapies for myeloma, there is a need for clinical trials investigating adjuvant therapies for high risk solitary plasmacytoma. We also suggest long‐term monitoring of solitary plasmacytoma patients due to the finding of late progression (>5 years) and the incidence of secondary cancers in this study.image