The spine is the most frequent site of bone metastasis, leading to considerable morbidities, including spinal pain and neurological dysfunction [1]. The management of spinal metastases requires a multidisciplinary approach including pharmacotherapy, radiation therapy, and surgery [2-4]. Surgery plays a valuable role in the management of intolerable pain, acquisition of structural stability, and restoration or preservation of neurological function [5].

The current development of surgical techniques has given rise to an expanding indication for surgery [6]. Minimally invasive surgery can be applied to patients with a short life expectancy and poor condition [7,8]. Proper prediction of postoperative prognosis is important when considering surgical indications. Tomita et al. [9], Tokuhashi et al. [10], and Katagiri et al. [11] have examined prognostic factors for patients with spinal metastasis. However, it is uncertain whether these prognostic factors are still applicable in the current situation with improvements in treatment modalities. Moreover, few reports have discussed prognostic factors in surgical treatment for spinal metastases in the 2010s. In this study, we examined survival and prognostic factors after surgery for a metastatic spinal tumor from 2010 to 2020.

Spinal metastasis is critical for patients, leading to substantial morbidities, including spinal pain and neurological dysfunction [1]. Surgery plays a valuable role in treatment to reduce pain, acquire structural stability, and restore or preserve neurological function [5]. Prediction of life expectancy in patients with spinal metastasis is important when determining the treatment option, particularly when surgery is considered. The Tomita score, Tokuhashi score, and new Katagiri score have been proposed and used over the years as prognostic factors for spinal metastasis [9-11].

However, recent studies have cast doubt on the validity of these scores, reporting the possibility that they do not reflect the prognosis with the improvement of treatment modalities [15]. Moreover, a study reported that primary tumor etiology and time elapsed since surgery should be considered when determining survival probability [16]. Conversely, the new Katagiri score was demonstrated to be a useful prognostic factor for patients undergoing surgery for spinal metastasis, even in recent cases [17]. The new Katagiri score is notable because it includes all bone and spinal metastases and takes into account the influence of the primary tumor and the efficacy of targeted and selective chemotherapy [11]. For these advantages, the new Katagiri score was selected for this study. In this study, the mean of the new Katagiri scores was 4.9, which was classified into intermediate-risk group, with overall survival rates of 71.0% at 6 months, 57.4% at 12, and 43.3% at 24. These results were not far from a previous report of survival rates of 74.0% at 6 months, 49.3% at 12, and 27.6% at 24 for patients with a prognostic score of 4–6 [11]. Moreover, the new Katagiri score was demonstrated to be a significant prognostic factor with HRs of 3.34 (95% CI, 2.10–5.32; p<0.01) for the intermediate-risk group and 7.77 (95% CI, 4.72–12.8; p<0.01) for the high-risk group, compared with the low-risk group. The new Katagiri score is still considered to greatly influence survival after surgical treatment of spinal metastases.

Frankel grade A was also associated with poor survival after surgery for spinal metastasis. The Frankel grade represents the degree of paralysis and is not a prognostic predictor. However, several studies have suggested a correlation between Frankel grade and survival period. According to Candido et al. [18], cases that did not improve from Frankel grade A, B, or C demonstrated statistically shorter survival than those who recovered to Frankel grade D or E: 7.89 months versus 19.13 months. Vanek et al. [19] reported that preoperative neurological status significantly influenced survival time; the median survival was 5.1 months in Frankel grades A–C and 28.2 months in Frankel grades D and E (p<0.001). Moreover, patients with Frankel grade A had a poor improvement rate in function after surgery [20]. Patients with Frankel grade A and severe motor deficits are less likely to achieve improvement in function, which may lead to medical complications and poor survival rates.

Although the ESCC scale and SINS were originally not used for indicating survival prognosis, relationships with survival have been proposed. Quraishi et al. [21] concluded that spinal surgery tended to result in more complications and worse survival in patients with higher grades of spinal cord compression. Whether SINS affects survival prognosis is controversial. Masuda et al. [22] reported that the median survival of the SINS unstable group (SINS ≥13) was statistically shorter than that of the unstable group, whereas other studies demonstrated no prognostic value of SINS for postoperative survival [23,24]. While older age is also expected to be associated with short survival after surgery, previous reports mentioned that compared with age <80 years, age >80 years was a risk factor only for poor improvement in neurological status and quality outcome but not for survival rates [20]. In this study, The ESCC scale, SINS, or age was not found to be a predictor for survival, and patients aged >80 years tended to survive longer than those aged <60 years with HR of 0.67 (95% CI, 0.33–1.34; p=0.26), although it was not significant. Patients with a good background, such as performance status and general condition, were limitedly extracted as participants because this study only focused on patients undergoing surgery.

In this study, ESCC scale 2 or 3 was noted in up to 79.0% (n=271) of patients, and intermediate or high risk of new Katagiri score in 73.5% (n=253), which could explain the increased incidence of complications. Complication rates after palliative spinal surgery remain high, ranging from 14% to 34% [25,26]. Systemic cancer treatment makes patients immunocompromised, and radiotherapy increases the risk of wound problems and infections. Patients also have a high risk of venous thromboembolism. In this study, the total complication rate was 39.1%, which was slightly higher than that in previous reports.

This study has some limitations. First, only patients who underwent surgery were enrolled. Second, owing to the retrospective analysis of data from multicenters, some clinical information was lacking, and surgical indications and procedures were not standardized among facilities. Third, nine facilities enrolled in this study were affiliated hospitals, resulting in limited indications or procedures of surgery that might not reflect current trends in Japan. Fourth, some patients had less than 1 month of follow-up by an orthopedic doctor, which may affect perioperative outcomes, including complications and survival rates. Finally, patient satisfaction and quality of life were not assessed. Patient satisfaction has been reported to be affected by neurological improvement [27], and further studies including these aspects are necessary to validate the efficacy of surgical treatment for spinal metastases.

Frankel grade A or intermediate or high risk in the new Katagiri score were significant prognostic factors associated with poor survival after surgery in patients with spinal metastases. Taking these factors into account is of great importance when considering treatment options for patients with spinal metastases. For better survival, chemotherapy or radiation therapy should be considered after surgery.