Prognostic factors for spinal chordomas and chondrosarcomas treated with postoperative pencil-beam scanning proton therapy: a large, single-institution experience

Objective: The aim of this paper was to evaluate the prognostic factors in surgical and adjuvant care for spinal chordomas and chondrosarcomas after surgery followed by high-dose pencil-beam scanning proton therapy (PBS-PT).

Methods: From 1997 to 2016, 155 patients (61 female patients; median age 55 years) with spinal (cervical, n = 61; thoracic, n = 29; lumbar, n = 13; sacral, n = 46; pelvic, n = 6) classic chordomas (n = 116) and chondrosarcomas (n = 39; most were low grade) were treated with maximal safe resection followed by PBS-PT (median dose prescribed: 74 Gy [relative biological effectiveness], range 48.6-77 Gy). The majority of patients (n = 153, 98.7%) had undergone at least 1 resection prior to PBS-PT (median 1, range 0-5; biopsy only, n = 2). Fewer than half (45.1%) of the surgeries were rated as gross-total resections (GTRs) prior to PBS-PT. Surgical stabilization (SS) was present in 39% of all patients (n = 60). Ninety-one patients (59%) presented with macroscopic tumor at the start of PBS-PT. The median follow-up duration was 64.7 months (range 12.2-204.8 months).

Results: The 5-year local tumor control, disease-free survival (DFS), and overall survival were 64.9% (95% CI 56.3%-73.5%), 59.4% (95% CI 50.6%-68.2%), and 77.9% (95% CI 70.6%-85.2%), respectively. In total, 63 patients (40.6%) experienced failure during the follow-up period: local only in 32 (20.6%), distal only in 7 (4.5%), local + distal in 19 (12.3%), surgical pathway failure (SPF) only in 2 (1.3%), local + SPF in 2 (1.3%), and distal + SPF in 1 (< 1%). Univariate analysis identified gross residual disease, the presence of SS, and treatment era prior to 2008 as highly significant for worse outcome, with all 3 remaining significant on multivariate analysis. The type of surgery (GTR or subtotal resection/biopsy) and whether GTR was achieved by en bloc or curettage did not show a significant prognostic effect. Surgical complications prior to PBS-PT were present in 42.5% of all surgically treated patients and were seen more commonly in patients with multiple surgical interventions (p = 0.005) and those operated on with the intent of en bloc resection (p = 0.006).

Conclusions: The extent of resection and metallic stabilization substantially influenced clinical outcomes for patients with spinal chordoma or chondrosarcoma despite high-dose adjuvant PBS-PT. Optimal upfront surgical management of these tumors continues to include GTR, as possible, with prompt adjuvant proton therapy.