Patient baseline characteristics
The clinical data of 49 patients with RRSC was described in Table 1. The population comprised 31 males and 18 females with a mean age of 44.2 years (median 37 y; range, 19-67 y). Of these patients, 27 patients with NOR of two times, and the remaining 22 patients experienced more than two times. Moreover, 16 patients were performed first operation in our hospital, and 33 patients underwent first surgical treatment in other hospitals. Of them, 10 RRSCs located in cervical spine, with 30 cases, 5 cases, and 4 cases in thoracic spine, lumber spine, and sacrum, respectively. 15 RRSCs was classified as Tomita I-III, and the other was classified as Tomita IV-VI, according to Tomita classification. Simultaneously, 24 patients were diagnosed as with conventional RRSC, 8 with mesenchymal variants, 14 with dedifferentiated subtype, and 3 with clear cell RRSC. All 49 patients underwent surgical treatment; total en bloc spondylectomy, total piecemeal spondylectomy, and subtotal resection were performed in 9, 23, and 17 cases, respectively. The surgical margin of 24 patients was narrow, while the remaining 25 cases were detected as wide margin.
Recurrence was detected in 33 patients after last surgical treatment, while 28 patients died during the follow-up period. The mean follow-up time was 31.7 months (median, 25 months; range, 5-93 months). The mean time from last surgery to recurrence was 13.4 months (median, 11 months; range, 3-68 months). while follow-up for the dead patients was 19.3 months (median, 16.5 months; range, 5–67 months).
Univariate analysis of prognostic factors affecting RFS and OS of patients with RRSC
Postoperative recurrence was common in patients with RRSC, the overall RFS rate after last surgical treatment was 32.7%, with mean RFS of 24.3 months (median, 17 months; range, 3-68 months). The detailed univariate analysis of prognostic factors for RFS was described in Table 1. In our series, the RFS of patients with tumor diagnosed as conventional subtype was longer than patients with other three subtypes, such as mesenchymal, dedifferentiated, and clear cell subtypes (p < 0.001). The recurrence rate was significantly different among patients with pathological grading I, II, and III (p < 0.001). In addition, intraoperative chemotherapy could obviously prolong the RFS of patients with RRSC (p = 0.080). Patients who experienced number of recurrence more than 2 times had shorter RFS than those underwent recurrence of 2 times (p < 0.001). Statistical results revealed that first surgical institution was our hospital could significantly increase the RFS of patients with RRSC (p = 0.032). Moreover, patients with wide surgical margin had high RFS rate than those with narrow surgical margin (p < 0.001).
Twenty-eight patients (57.1%) suffered death, thus the OS for RRSC was 42.9%, with mean OS of 31.7 months (median, 25 months; range, 5-93 months). Univariate analysis of prognostic factors affecting OS was shown in Table 1. According to statistical results using log-rank test, a significant difference was found in patients’ age (p = 0.079), histological subtype (p < 0.001), pathological grading (p < 0.001), postoperative radiotherapy (p = 0.077), NOS (p < 0.001), FSI (p = 0.078), and surgical margin (p < 0.001), respectively.
Multivariate analysis of prognostic factors affecting RFS and OS of patients with RRSC
Potential prognostic factors extracted by univariate analysis were submitted to Cox proportional hazards analysis. Multivariate analysis of potential independent prognostic factors of RFS was shown in detail in Table 2. NOR was significantly associated with RFS of patients with RRSC (The hazard ratio [HR] was 0.240, p = 0.012). Patients with wide surgical margin had longer RFS rate than those with narrow surgical margin (HR, 3.194; p = 0.002). The Kaplan-Meier curves of RFS for NOR and surgical margin were shown in Fig. 2. Moreover, the results of multivariate analysis of prognostic value for OS revealed that pathological grading and surgical margin were significant prognostic factors for OS of patients with RRSC in Table 3 (pathological grading: HR, 3.283; p = 0.012 and surgical margin: HR, 0.216; p = 0.008). And the Kaplan-Meier curves of OS for pathological grading and surgical margin were described in Fig.3.
Baseline characteristics of patients underwent five surgical treatment
Of all patients, 27 patients underwent two-times recurrence, 15 patients with three times, 7 patients with four times. The detailed baseline characteristics of seven patients underwent four-time recurrences were described in Table 4. Of them, only one patient (case# 3) had first surgical treatment in our hospital after initial diagnosis. Thoracic spine was the most common location of lesion of RRSC with four recurrences. Only one tumor was classified as Tomita III according to radiological result (case# 1). Two patients (case# 2,4) experienced postoperative radiotherapy were dead during follow up. All patients with tumor evaluated as dedifferentiated spinal chondrosarcoma and pathological grading III were dead, while only one patient (case# 3) was alive with disease and one patient (case# 7) lived with no evidence of disease.