Solitary plasmacytoma (SP) is a malignant tumor caused by monoclonal proliferation of plasma cells, accounting for about 3–5% of all plasma cell neoplasms (1, 2). SP can be divided into extramedullary plasmacytoma (EMP) and solitary bone plasmacytoma (SBP). SPB accounts for 60–70% of SP, mainly in the red marrow-containing bone, especially vertebrae and femurs (3, 4). SPB patients may experience bone pain, neurological symptoms, and pathological fractures, but lack multiple myelomas (MM) characteristics such as multiple lytic bone lesions, hypercalcemia, and renal insufficiency (5).

Studies have reported that older age, the primary site of the tumor, developing MM, histologic grade, treatment methods, and posttreatment persistent M protein were significant prognostic factors of SPB (6–12). Among them, age plays an important role in the prognosis of SPB patients. Studies have showed that age > 60 years was an important risk factor for the worse OS (13, 14) and progression to MM (14) in SPB patients. Similarly, older age (≥65 years) is significantly associated with the worse OS compared to younger SPB patients (1). Elderly SPB patients are more likely to receive palliative care rather than cure treatment. And older patients are more likely to be intolerant of radical radiation therapy than their younger counterparts (15). Meanwhile, elderly patients are more likely to be frail or have comorbidity. These factors may affect the survival of SPB patients. Therefore, it has a clinically important role in predicting the survival of elderly SPB patients.

Therefore, based on the SEER database, we collect data from a large number of patients to develop a survival prediction nomogram and a risk-stratifying system that can dynamically predict the long-term survival of elderly SPB.

The SEER database covers a great number of cancer cases with complete follow-up. It is often used in combination with nomograms to predict the survival of cancers (16, 17). We included 1,179 elderly SPB patients to analyze clinical and demographic sociology-related prognostic factors. Then we built a nomogram to predict the OS of elderly SPB patients. The nomogram was based on five independent risk factors: age, marital status, prior cancer, radiotherapy, and chemotherapy. And with the increase of age, the immune system's ability continues to decline, which may cause tumor deterioration or serious treatment complications, reducing the patient's survival time. Older patients often have more comorbidities such as diabetes, cardiovascular and cerebrovascular diseases, and other cancers than younger patients. It may directly have a negative impact on survival or affect treatment tolerance (18). Also, in this study, prior cancer before SPB and older age are the negative factors in elderly patients with SPB.

Marital status is a significant prognostic factor for many cancers (19–21). Compared with unmarried or divorced patients, married patients may get better financial, emotional support, and life care from their partners or family members. Therefore, it may be associated with a better prognosis. Similarly, we found that married was a favorable prognostic factor for OS in SPB patients.

Radiotherapy, surgery, and systematic chemotherapy are the commonly used treatments for SPB. The guidelines recommend that the standard treatment of SPB is local radiotherapy (22, 23). Local radiotherapy can provide good local control and survival for SPB patients (11, 24, 25). And our study reaffirmed the benefits of radiotherapy for SPB patients. We found that radiotherapy was the primary treatment, and 78.8% of patients received radiotherapy. Radiotherapy can significantly improve the OS of SPB patients.

Guidelines recommend that surgery may be considered when SPB patients have a structural imbalance or neurological damage caused by tumor (22). Our results suggested that surgery does not affect patient outcomes. Surgery can only relieve symptoms of SPB patients and improve their self-care ability, but it may not stop the progression of the SPB.

Currently, adjuvant chemotherapy is not recommended due to insufficient research support. Several previous multicenter studies have shown that chemotherapy does not benefit the survival of SPB patients (14, 26, 27). A recent survey by Khaled et al. shows that the addition of chemotherapy mainly based on bortezomib/dexamethasone or lenalidomide/dexamethasone improves multiple myeloma-free survival and PFS in patients with SPB (28). However, it was retrospective studies of a small sample, and additional adjuvant chemotherapy did not improve the survival of SPB in most previous studies. More evidence is needed in the future. In our study, 236 (20.0%) patients received chemotherapy. The results showed that chemotherapy is an adverse prognostic factor. The following reasons should be considered: chemotherapy is often used in patients who are intolerant to radiotherapy or have the potential risk of developing MM. The prognosis of those SPB patients is often poor. Besides, we must acknowledge that there is no detailed information about chemotherapy regimens in our data, and we cannot compare the effects of different chemotherapy regimens on survival. It may lead to biased final results.

However, some limitations of our research should be noted. Firstly, it was a retrospective study, and the potential selection bias was unavoidable. Secondly, since detailed treatment data such as chemotherapy and radiotherapy regimens cannot be obtained from the SEER database, the treatment effect cannot be further evaluated. Third, much clinical and pathological information, such as the extent of bone marrow involvement and the M protein in blood/urine cannot be obtained, which may lead to study bias.

Undeniably, it was a large population-based study, and its results were representative. Then, we constructed an effective nomogram to evaluate the OS of elderly SPB patients. The excellent performance of the nomogram has been confirmed by ROC curves, calibration curves, and decision curve analysis.

In summary, the novel nomogram and risk-stratifying system could effectively predict long-term OS in elderly patients with SPB and identify high-risk patients. It is of great significance to improve the prognosis of patients.

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.

YW and JC designed the main study. JW and SC collected and analyzed the data. YW and XL made contributions to the drafting of the manuscript. JC contributed substantially to the revision of the manuscript. All authors have read and approved the final draft of the manuscript.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.