Evaluating TNM stage prognostic ability in a population-based cohort of gastric adenocarcinoma patients in a low-incidence country

Objectives — TNM stage is the preeminent cancer staging system and a fundamental determinant of disease prognosis. Our goal was to evaluate the predictive power of TNM stage for gastric adenocarcinoma (GAC), in a low-incidence country.

Methods — A province-wide chart review of GAC patients diagnosed from April 1, 2005 to March 31, 2008 was conducted in Ontario and linked to routinely collected vital status data with a follow-up on March 31, 2012. TNM staging was classified using the sixth and seventh Union International for Cancer Control/American Joint Committee on Cancer editions. Kaplan-Meier and log-rank tests compared stage-stratified survival estimates. Discrimination was evaluated using Harrell's C statistic.

Results — The cohort included 2366 patients. One- and 5-year survival was 43% and 17%. Using the sixth edition, 9% of patients had stage I disease, 5.4% stage II, 7.3% stage III, and 64% stage IV; 15% were not staged. Using the seventh edition, 9% were stage I, 7.7% stage II, 16% stage III, and 54% stage IV; 14% were not staged. Stage-stratified 5-year survival ranged from 68% to 7% with the sixth edition and from 70% to 4% with the seventh edition. Harrell's C statistic was 0.64 (0.63-0.65) for the broad sixth edition staging categories and 0.68 (0.67-0.69) for the broad seventh edition. Discriminative power was similar for the refined stage categories and across multiple subgroup analyses; it was best in non-metastatic patients.

Conclusions — Existing staging systems for GAC used in North America predict individualized prognosis poorly. The creation of a more complex prediction tool is necessary to provide accurate and precise prognostication information to oncologists, patients, and their families.