ASO Author Reflections: Location-Specific Staging in Sarcoma—A Step in the Right Direction

PAST

A staging system that accurately categorizes groups of patients, communicates specific information about pertinent factors, and prognosticates outcomes is a critical component of cancer care.¹ Given the diversity of location and > 70 histologic subtypes, soft tissue sarcoma (STS) represents a problematic area of cancer staging. Since its inception in 1992 until recently, with the introduction of the 8th edition of the American Joint Committee on Cancer (AJCC) staging system, staging for STS combined tumors from all anatomic sites spanning all histologies. Wide variation in tumor size makes establishing a meaningful tumor (T) stage system difficult. The node (N) category is less meaningful for most STSs as lymph node metastases are rare.² In addition to the standard T, N, and metastasis (M) categories, sarcoma staging incorporates grade (G). However, the presence of multiple different grading schemas, as well as changes in terminology over time, contribute to an already heterogeneous system, making STS staging particularly difficult.

PRESENT

To address these issues, the AJCC 8th edition³ created STS staging systems unique to tumor location, expanded the T-stage category, removed tumor depth, and redefined nodal disease as M1/stage IV. We used the National Cancer Database to evaluate the prognostic power of the 8th edition for STS of the trunk/extremities.⁴ The construction of additional T categories better reflected the characteristics of the population (median 7.7 cm) and allowed more even incremental changes in 5-year overall survival between stages (85.3% IA, 83.0% IB, 79.0% II, 62.4% IIIA, 50.1% IIIB, 13.9% IV). As tumor size increased, there was less of an impact on survival, with similar outcomes between patients with T3 (10 cm < T≤15 cm) and T4 (> 15 cm) tumors. Although only a small proportion of patients had isolated nodal disease (211/26,144), grouping them with patients with distant metastases is not representative—5-year overall survival (33.1%) was better than patients with distant metastases (12.4%), but inferior to patients with stage IIIB disease (50.1%).

FUTURE

The introduction of staging unique to tumor site is a huge advancement. However, histology remains an important unaccounted for factor in STS. One strength of our study, i.e. its ability to assess outcomes across a large population treated at representative cancer centers, is also a weakness. Central pathologic review is impossible, and STSs comprise diverse histologies at high risk for diagnostic error and muddied by changes in grading schema and terminology, making it impossible to analyze the impact of histology on outcome. Sarcoma-specific nomograms that incorporate histology and other prognostic factors not captured in a traditional staging system offer valuable information for individual patients,⁵ and their use is encouraged. Construction of histology-specific staging for each STS subtype is impractical; future attempts to account for histology may group similar histologies together. Finally, we suggest that future iterations of extremity and trunk STS staging allow for separate classification of patients with isolated nodal disease as outcomes differ from those with disseminated metastatic disease.