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Comment & Response
November 14, 2018

Interpreting the Long-term Prognostic Value of Total Mesorectal Excision Plane Quality in Rectal Adenocarcinoma

Author Affiliations
  • 1Department of Biostatistics, Harvard T. H. Chan School of Public Health, Boston, Massachusetts
  • 2Department of Pathology and Laboratory Medicine, Albany Medical College, Albany, New York
JAMA Surg. Published online November 14, 2018. doi:10.1001/jamasurg.2018.3540

To the Editor Kitz et al1 evaluated the prognostic value of total mesorectal excision (TME) plane in patients with rectal cancer. Total mesorectal excision plane quality was grouped into 3 categories: mesorectal, intramesorectal, and muscularis propria. One end point was disease-free survival (DFS). The authors quantified the between-group differences using 3-year event-free rates and hazard ratios (HRs). Three-year DFS rate estimates for mesorectal, intramesorectal, and muscularis propria TME were 75.9% (95% CI, 73.1-78.8), 68.4% (95% CI, 61.6-76.0), and 67.2% (95% CI, 55.6-81.3), respectively. Because these confidence intervals overlap, it is unclear whether there is a true difference between certain pairs, eg, between intramesorectal and muscularis propria TME. Moreover, in Figure 2A,1 the DFS curves extend up to 60 months. Thus, the 3-year event rate provides a local profile of DFS only. To use data after 3 years, the authors reported HRs for DFS (intramesorectal vs mesorectal TME: HR, 1.35; 95% CI, 1.01-1.80; muscularis propria vs mesorectal TME: HR, 1.73; 95% CI, 1.13-2.66). However, it is difficult to interpret HRs in the clinical context. The hazard is not a chance or probability measure and therefore is not equivalent to risk. Thus, an HR of 1.35 cannot be translated into a 35% risk increase. Also, no reference hazard value from mesorectal TME was provided. If mesorectal TME hazard is low, a 35% increase in hazard may not be clinically significant. Other issues and concerns in using HRs to quantify between-group differences have been discussed extensively.2-4

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