Surgery combined with radiotherapy for the treatment of solitary plasmacytoma of the rib: a case report and review of the literature

Solitary plasmacytoma of the bone, especially of a single rib, is a rare disease. We present the case of a 44-year-old Han Chinese man who was diagnosed with a solitary plasmacytoma of the bone located in the right sixth rib. The patient presented with a 4-year history of continuous pain in the right chest area and moderate fever lasting 7 days. A chest roentgenogram showed a solitary expanding lesion in the right thorax, and chest computed tomography revealed an osteolytic tumor in the chest wall. The patient underwent complete en-bloc resection of the chest wall, including the ribs, muscle, and parietal pleura. Histologically, the resected mass was composed of abundant neoplastic plasma cells, and the diagnosis was confirmed to be a plasmacytoma of rib. The examination of marrow cells showed 9 % normal plasma cells among karyocytes without clonal disease. On postoperative day 14, the patient underwent thoracic radiotherapy with a total dose of 50 Gy. The patient remained asymptomatic during the 6-month follow-up period. Herein, we also review previous reports on solitary plasmacytomas of the rib. In summary, this report provides further insights for the diagnosis and effective treatment of this rare disease.


Background
Solitary plasmacytoma of bone (SPB) is a rare localized neoplasm that accounts for only 5 % of malignant plasma cell tumors [1]. SPBs typically occur in the vertebrae or pelvic bones, with presentation in the rib being less common [2,3]. SPBs are characterized by the presence of only one or two isolated bone lesions with no evidence of disease dissemination and are generally considered to be curable with surgical resection and radiotherapy [4]. In most cases, SPBs present as osteolytic lesions of the bone on chest X-ray [5]. Herein, we report a case of solitary plasmacytoma of the rib (SPR) with unique clinical features.

Case report
A 44-year-old man visited our clinic complaining of continuous pain in the right chest area for 4 years and moderate fever for 7 days. He had no history of trauma or tuberculosis. A chest roentgenogram (Fig. 1a) and chest computed tomography (CT) ( Fig. 2a and b) revealed a 6.11 cm × 9.33 cm, oval opacity in the right side of the chest, which was highly suspected to be an intrathoracic tumor originating from the pleura or rib. Spiral CT three-dimensional reconstruction showed an osteolytic lesion in the right sixth rib ( Fig. 2c and d), and abnormally increased uptake of radioisotope around the right sixth rib was observed in a bone scan (Fig. 1b). The radiologic features suggested a focal lytic lesion in the right sixth rib and limited pleura thickening ( Fig. 2a  and b). Peripheral blood examination showed no abnormalities (Table 1). Therefore, we decided to remove the lesion via a surgical approach for the treatment and diagnosis of the tumor. A standard posterolateral thoracotomy was performed along the fifth intercostal space. We completely resected the tumor and the surrounding fifth and seventh ribs with a safety margin of at least 3 cm. Adherent parietal pleura at the tumor site was also resected. During the operation, no pleural dissemination was found. Reconstruction of the chest wall defect was accomplished using a tension-free dacron patch (Johnson & Johnson, New Brunswick, NJ, USA). The gross pathology of the resected specimen showed an irregular, pale, soft, and friable tumor (Fig. 3a). Histological analysis of the resected tumor revealed abundant neoplastic plasma cells in the lesion (Fig. 3b). Immunohistochemical staining of the specimen showed positive staining for CD38 and CD138 ( Fig. 3c and d). No M-protein in the serum or urine was found by immunoelectrophoresis. A biopsy of the bone marrow along with aspiration revealed that normal plasma cells accounted for 9 % of karyocytes, and these cells expressed CD38, CD138, CD19, and CD45 (Table 1). These characteristics were consistent with a diagnosis of plasmacytoma, excluding the possibility of multiple myeloma (MM).
Starting in postoperative day 15, radiation therapy with a total target dose of 50 Gy (2 Gy/d, 25 days) was administered to tissue surrounding the area of the resected tumor. The patient was followed up at 6 months after surgery and was relapse-free with no recurrence according to a chest CT scan (Fig. 4).
The currently recommended diagnostic criteria [5] for SPB include the following: (i) clinical and radiological evidence of a single area of bone destruction on skeletal survey; (ii) histological confirmation of plasma cell histology; (iii) normal marrow without clonal disease; (iv) absence of anemia, hypercalcemia, or renal impairment attributable to myeloma; and (v) absent or low serum or urinary level of monoclonal protein (called Bence-Jones protein) and preserved levels of uninvolved immunoglobulins. Therefore, the diagnosis of our case was based on the following findings: osteolytic rib observed by imaging, histopathological  Surgical intervention is the first choice of treatment for SPB, and a complete resection is expected to be curative. Bataille et al. [1] reported 114 cases of solitary myeloma and showed that the lowest incidence of progressive disease was observed in patients with peripheral solitary plasmacytoma treated with surgery plus an adequate dose of radiation therapy. Aviles et al. [26] demonstrated that most patients treated with adequate radiation therapy alone will develop MM within 3 years. With respect to the radiation dose, Mendenhall et al. [27] reported that the local failure rates were 6 and 31 % in patients with a solitary plasmacytoma treated with doses of 40 Gy or greater and doses below 40 Gy, respectively. It is recommended that SPB be treated with radical radiotherapy, encompassing the tumor volume shown on magnetic resonance imaging with a margin of at least 2 cm and treated to a dose of 40 Gy in 20 fractions. For a SPB with a tumor size of >5 cm, a higher dose of up to 50 Gy in 25 fractions should be considered [7].
The role of adjuvant chemotherapy in preventing progression to MM remains unclear. Some reports suggest that adjuvant chemotherapy does not affect the incidence of conversion from SPB into MM but could delay its progression to MM [4]. Patients not responsive to radiotherapy could be treated with chemotherapy, with a similar approach to that used in the treatment of MM [7], but the effectiveness of chemotherapy for SPR remains to be determined. Our patient received a complete en-bloc resection and postoperative 50 Gy of radiotherapy, with no relapse at 6 months after surgery,  indicating that our surgery plus radiation therapy was efficacious. It is generally accepted that patients with SPB have an indolent course of disease, with a median survival time of 10.7 years and 5-, 10-, and 20-year survival rates of 75, 52, and 37 %, respectively [5]. However, Warsame et al. [28] reported that in a study of 127 SPB patients followed up for 7-28 months (median, 56 months), 85 patients (67 %) progressed to MM and 27 patients (21 %) died of progression.

Conclusion
In conclusion, SPRs show an earlier average age of onset and higher male to female incidence ratio than SPBs located in other bones, according to the literature review. SPRs should be considered when confronted with a lytic tumor of the rib. The treatment is based on surgery and radiotherapy. SPRs are often resectable, and the prognosis is generally good and dominated by the risk of progression to MM.

Consent
Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.

Competing interests
The authors declare that they have no competing interests.
Authors' contributions ZFZ, study concept and design; RJ and LX, drafting and finalization of the manuscript, preparation of the figures, acquisition of data, and analysis and interpretation of data; KG, HGL and JL, critical revision of the manuscript for important intellectual content and material support; and all authors read and approved the final manuscript.