AJCC eighth edition for soft tissue sarcoma of the extremities and trunk
Authors: J.M.M. Cates
Journal: Annals of Oncology (2018)

To the Editor, A recent editorial written by Dr Sam Yoon, the lead author of the American Joint Committee of Cancer (AJCC) 8th edition for soft tissue sarcoma of the extremities and trunk, warrants a formal response [1.Yoon S.S. The new American Joint Commission on Cancer staging system for soft tissue sarcomas: splitting versus lumping.Ann Surg Oncol. 2018; 25: 1101-1102Crossref PubMed Scopus (9) Google Scholar]. From the nature of his comments, I question whether Dr Yoon fully comprehends the implications of two recent studies comparing the seventh and eighth editions of the staging algorithms for soft tissue sarcoma [2.Fisher S.B. Chiang Y.J. Feig B.W. et al.Comparative performance of the 7th and 8th editions of the American Joint Committee on Cancer staging systems for soft tissue sarcoma of the trunk and extremities.Ann Surg Oncol. 2018; 25: 1126-1132Crossref PubMed Scopus (23) Google Scholar, 3.Cates J.M.M. The AJCC 8th edition staging system for soft tissue sarcoma of the extremities or trunk: a cohort study of the SEER database.J Natl Compr Canc Netw. 2018; 16: 144-152Crossref PubMed Scopus (62) Google Scholar]. In his editorial, he states that 'overall stage groupings (in the eighth edition) have better discrimination in terms of overall survival'. Direct pairwise comparisons of the associated hazard ratios for each stage category argue against this assertion [3.Cates J.M.M. The AJCC 8th edition staging system for soft tissue sarcoma of the extremities or trunk: a cohort study of the SEER database.J Natl Compr Canc Netw. 2018; 16: 144-152Crossref PubMed Scopus (62) Google Scholar]. The new staging system simply exchanges limited discriminatory power between stages IIA and IIB in the seventh edition for limited discrimination between stages II and IIIA in the eighth edition. Furthermore, the methodological critiques of the MD Anderson Cancer Center study offered by Dr Yoon are specious for multiple reasons (unfortunately, space limitations preclude elaboration in this format). Dr Yoon concludes that 'the eighth edition of the AJCC staging system for soft tissue sarcoma improves on prior editions' [1.Yoon S.S. The new American Joint Commission on Cancer staging system for soft tissue sarcomas: splitting versus lumping.Ann Surg Oncol. 2018; 25: 1101-1102Crossref PubMed Scopus (9) Google Scholar]. Two recent studies, including the one he editorializes, argue the contrary—that the eighth edition staging system does not improve prognostic accuracy compared with the prior seventh edition [2.Fisher S.B. Chiang Y.J. Feig B.W. et al.Comparative performance of the 7th and 8th editions of the American Joint Committee on Cancer staging systems for soft tissue sarcoma of the trunk and extremities.Ann Surg Oncol. 2018; 25: 1126-1132Crossref PubMed Scopus (23) Google Scholar, 3.Cates J.M.M. The AJCC 8th edition staging system for soft tissue sarcoma of the extremities or trunk: a cohort study of the SEER database.J Natl Compr Canc Netw. 2018; 16: 144-152Crossref PubMed Scopus (62) Google Scholar]. The above disagreements aside, I concur with Dr Yoon's opinion that 'the AJCC eighth edition staging system for soft tissue sarcoma represents a significant advance in terms of now grouping tumours by location' [3.Cates J.M.M. The AJCC 8th edition staging system for soft tissue sarcoma of the extremities or trunk: a cohort study of the SEER database.J Natl Compr Canc Netw. 2018; 16: 144-152Crossref PubMed Scopus (62) Google Scholar, 4.Cates J.M.M. Performance analysis of the American Joint Committee on Cancer 8th edition staging system for retroperitoneal sarcoma and development of a new staging algorithm for sarcoma-specific survival.Ann Surg Oncol. 2017; 24: 3880-3887Crossref PubMed Scopus (19) Google Scholar]. Anatomic site-specific staging algorithms for soft tissue sarcoma were long overdue. However, as the MD Anderson Cancer Center group and I have recently demonstrated, the challenge for the AJCC now is to optimize the newly proposed site-specific staging schema. Stratifying patient risk by categorizing an intrinsically continuous variable (tumour size) can lead to misspecification in predictive models [5.Cates J.M.M. Modeling continuous prognostic factors in survival analysis: implications for tumor staging and assessing chemotherapy effect in osteosarcoma.Am J Surg Pathol. 2018; 42: 485-491Crossref PubMed Scopus (18) Google Scholar]. I personally do not foresee an easy solution, since unlike several other organ systems, soft tissue sarcomas lack well-defined anatomic boundaries by which to 'ordinalize' local tumour extent. For now, judicious cut-point determinations of tumour size for risk stratification must be based on rigorous statistical analysis of the data currently available (and not limited to relatively small single institutional cohorts). The eighth edition of the AJCC staging system for soft tissue sarcoma of the extremities and trunk fails in this regard. None declared.