Clinical investigation
Bone
Outcomes and patterns of failure in solitary plasmacytoma: A multicenter Rare Cancer Network study of 258 patients

Presented at the 39th Annual Meeting of the American Society of Clinical Oncology, Chicago, IL, May 31 to June 3, 2003; the 12th European Cancer Conference, Copenhagen, Denmark, September 21–25, 2003; and the 45th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO), Salt Lake City, UT, October 19–23, 2003.
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Purpose: To assess the outcomes and patterns of failure in solitary plasmacytoma (SP).

Methods and Materials: The data from 258 patients with bone (n = 206) or extramedullary (n = 52) SP without evidence of multiple myeloma (MM) were collected. A histopathologic diagnosis was obtained for all patients. Most (n = 214) of the patients received radiotherapy (RT) alone; 34 received chemotherapy and RT, and 8 surgery alone. The median radiation dose was 40 Gy. The median follow-up was 56 months (range 7–245).

Results: The median time to MM development was 21 months (range 2–135), with a 5-year probability of 45%. The 5-year overall survival, disease-free survival, and local control rate was 74%, 50%, and 86%, respectively. On multivariate analyses, the favorable factors were younger age and tumor size <4 cm for survival; younger age, extramedullary localization, and RT for disease-free survival; and small tumor and RT for local control. Bone localization was the only predictor of MM development. No dose–response relationship was found for doses >30 Gy, even for larger tumors.

Conclusion: Progression to MM remains the main problem. Patients with extramedullary SP had the best outcomes, especially when treated with moderate-dose RT. Chemotherapy and/or novel therapies should be investigated for bone or bulky extramedullary SP.

Introduction

Solitary plasmacytoma (SP) is defined as a proliferation of monoclonal plasma cells without evidence of significant bone-marrow plasma-cell infiltration. It constitutes about 5% of cases of plasma-cell myeloma (1). Two separate entities have been categorized, dependent on the lesion originating in either bone or extramedullary soft tissue (2).

Given the lack of randomized trials in this rare, but radiosensitive, disease (3), recommendations for the choice of treatment have been mainly based on data from retrospective studies, which often had relatively small numbers of patients and a limited ability to make any robust conclusions (4, 5). Only one prospective study included 53 patients (6).

Several studies have shown that radiotherapy (RT) for SP is very effective in providing local control and cure. However, with respect to long-term outcomes, it is known that bone SP progresses more frequently to multiple myeloma (MM) than does soft-tissue SP (7, 8, 9).

No conclusive data have been published on the optimal radiation dose for SP. Many authors have reported a wide range of doses varying from 30 to 66 Gy (10, 11, 12). No evidence has shown whether a radiation dose >30 Gy improves the outcomes. However, most centers use ≥50 Gy to treat SP.

We report the results of a retrospective multicenter study of a large cohort of patients with SP from 19 European and North American centers, aiming to assess the treatment approaches; radiation dose–response effects; and different prognostic factors for survival, progression to MM, and patterns of local failure.

Section snippets

Methods and materials

Between 1977 and 2001, 258 adult patients consecutively treated for bone (n = 206) or extramedullary (n = 52) SP without evidence of MM were collected in a retrospective multicenter study of the Rare Cancer Network. All patients with a new diagnosis of SP and considered candidates for definitive management with curative intent were included in this study. A patient was considered to have SP if the following criteria were met: biopsy-proven solitary lesion, <10% plasma cells in the bone marrow

Local control

Local relapse was observed in 14% of the patients (n = 36), with a median time to local relapse of 20 months (range, 4–149). No regional lymph node relapse was observed. The 5- and 10-year probability of local control was 86% (95% CI, 81–91) and 78% (95% CI, 69–87), respectively. The 10-year local control rate according to radiation dose and other candidate factors is shown in Table 2, Table 3. Local control was better with small tumors (<4 cm) and in patients treated with RT; however, no

Discussion

Prognostic factors, including age, tumor size, and location of origin (extramedullary vs. bone), have been reported to influence the outcomes of SP patients in several series (2, 8, 10, 12, 19, 20, 21, 22).

Despite good local control with RT, patients with bone SP progress to MM more frequently than those with extramedullary SP (7, 10). Many questions remain unanswered about the prognostic factors influencing the outcomes and radiation dose–response relationship, probably because of the limited

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