Cancer is one of the most common causes of death in elderly patients. The morbidity and mortality of bone tumors are high. A study have reported that there are 3,600 new bone tumor patients in the United States each year, and 1,720 deaths from bone tumors. Although MBT are not common, their mortality is still at a high level. The three most common MBT in elderly patients include chondrosarcoma, osteosarcoma, and chord sarcoma, of which chondrosarcoma is the most common[5, 6]. Our study also found that most of the elderly patients with MBT over 60 years old are chondrosarcoma. Giuffrida et al. found that there are huge differences in the 5-year survival rate of patients with different subtypes of chondrosarcoma. The 5-year survival rate of dedifferentiated chondrosarcoma is 0%, while the clear cell type reaches 100%, the mucinous type is 71%, the paracortical type is 93%, the mesenchymal chondrosarcoma is 48%, and the malignant chondroblastoma is 85%. Strotman et al. found that the 5-year overall survival rate of dedifferentiated chondrosarcoma is only 18%, and the prognosis is worse for patients with axial bone, tumor size greater than 8 cm, and lung metastasis . Study by Bielack et al. showed that age, location, and metastasis are the prognostic factors of patients with osteosarcoma. Previous studies have reported the prognostic factors of osteosarcoma and predicted overall survival and cancer-specific survival[23, 24]. Chord sarcoma is also a malignant bone tumor with high incidence in elderly patients. Previous studies have reported that chordoma mainly occurs in patients over 30 years old, and most of them are people over 60 years old. Chord sarcoma rarely metastasizes, but once a distant metastasis occurs, the 5-year survival rate will drop to about 50%. The incidence and prognostic factors of MBT in elderly patients have not yet been reported in the literature. Accurate prediction of patient survival is conducive to future treatment and follow-up. Therefore, we developed and validated nomograms to predict the survival of elderly patients with MBT.
In our study, we found that the increase in age will reduce the survival rate of elderly patients. Previous studies have also reported that age is a risk factor for bone tumors[24, 27]. The reason may be that the increase in age leads to a decrease in the suppression of tumors by the immune system and an increase in the probability of comorbidities. In addition, our study also found that the tumor site and size are also important factors affecting the prognosis. Similar to previous studies, patients with axial and large tumors have a higher risk of death[28–30]. It may be because larger tumors are more likely to metastasize, and tumors in the axial position, especially those of the spine, are more likely to metastasize and invade surrounding tissues. Previous studies have found that tumor stage is also an important risk factor. The prognosis of distantly metastatic tumors is worse than that of localized tumors[32, 33]. Our study also found that tumor stage is an independent risk factor for prognosis. Besides, we found that sex and race are also important risk factors, which seems to have not been found in previous studies. Women have a better survival prognosis than men. American Indian and Asian seem to have higher survival rates than whites and blacks.
In this study, we found that surgery significantly improved the prognosis of patients, similar to the results of previous studies[34, 35]. In addition, according to risk stratification, we found that patients in the high-risk group benefited the most from partial tumor resection, while there is no significant difference in the prognosis of patients in the low-risk group with various treatment methods. Since most of the patients in the high-risk group are in the late stage of the disease and have already developed distant metastases, radical resection does not seem to improve the prognosis of the patients. This has some enlightenment for doctors and patients in choosing surgical methods for patients with different risks. On chemotherapy, our study found that chemotherapy has no effect on patient survival, similar to previous studies.
Although our nomogram includes three histological types of MBT, it has been validated that the prediction model has good accuracy and discrimination. The C-index of the training set and the validation set were 0.779[0.759-0.799] and 0.801[0.772-0.830], respectively, proved the discriminative ability of the nomogram. The predicted value of the calibration curve is highly consistent with the observed value, which indicates the accuracy of the prediction model. We compared the 1-, 3-, and 5-year DCA of the nomogram with the traditional TNM staging system and proved that the clinical value of the nomogram is higher than that of the traditional TNM staging system. Risk stratification also accurately distinguished high-risk and low-risk patients, and treatment and follow-up strategies should be different for patients in different risk groups. Patients in the high-risk group should choose appropriate treatment and receive closer follow-up.
However, our study still has some limitations. First, the SEER database cannot obtain detailed information on some variables such as surgical margins, BMI, smoking and drinking, so it has a certain impact on the accuracy of prediction. However, we include important variables such as tumor stage, size, surgery and other factors that affect the prognosis of patients, so that the results will not cause a devastating deviation. Second, The lack of information on some important variables will cause errors in the prediction results. For example, the tumor grade of some patients is unknown. However, it can be seen from the nomogram that the lack of tumor grade of some patients did not cause serious bias. Finally, our nomogram has only been validated internally, external validation is necessary to test the predictive power of the nomogram.