Incorporating Tumor Characteristics to the American Joint Committee on Cancer Breast Cancer Staging System.

BACKGROUND: The American Joint Committee on Cancer (AJCC) breast cancer staging system provides important prognostic information. The recently published eighth edition incorporates biological markers and recommends the use of a complex "prognostic stage." In this study, we assessed the relationship between stage, breast cancer subtype, grade, and outcome in a large population-based cohort and evaluated a risk score system incorporating tumor characteristic to the AJCC anatomic staging system.
MATERIALS AND METHODS: Patients diagnosed with primary breast cancer stage I-IV between 2005-2008 were identified in the California Cancer Registry. For patients with stage I-III disease, pathologic stage was recorded. For patients with stage IV disease, clinical stage was utilized. Five-year breast cancer specific survival (BCSS) and overall survival (OS) rates were determined for each potential tumor size-node involvement-metastases (TNM) combination according to breast cancer subtype. A risk score point-based system using grade, estrogen receptor, and human epidermal growth factor receptor 2 (HER2) status was designed to complement the anatomic AJCC staging system. Survival probabilities between groups were compared using log-rank test. Cox proportional hazards models were used.
RESULTS: Among 43,938 patients, we observed differences in 5-year BCSS and OS for each TNM combination according to breast cancer subtype. The most favorable outcomes were seen for hormone receptor-positive tumors followed closely by HER2-positive tumors, with the worst outcomes observed for triple negative breast cancer. Our risk score system separated patients into four risk groups within each stage category (all p < .05).
CONCLUSION: Our simple risk score system incorporates biological factors into the AJCC anatomic staging system, providing accurate prognostic information. IMPLICATIONS FOR PRACTICE: This study demonstrates that stage, but also breast cancer subtype and grade, define prognosis in a large population of breast cancer patients. It shows that a point-based risk score system that incorporates these biological factors provides refined stratification and information on prognosis, improving the anatomic American Joint Committee on Cancer (AJCC) staging system. In addition, the overall mortality and breast cancer specific mortality rates detailed here provide much-needed information about prognosis in the current era, refining the current AJCC staging. © AlphaMed Press 2017.