Reclassification of stages leads to changes of relative survival rates: The new TNM classification for breast cancer

Purpose: The 6th edition of TNM classification, valid since January 1, 2003, shows important changes in breast cancer classification, especially regarding lymph node status and UICC stage grouping. The effects of the redefinition of the TNM categories on stage and prognosis have not yet been studied in a large cohort of patients. Patients and Methods: We analyzed TNM staging of 5366 breast cancer cases registered at the Gynecological University Hospital Heidelberg (diagnosed from 1985 to 2000) according to the old and the new TNM classification. The effects of the new classification system were examined with regard to stage grouping and survival. Results: One of the most important effects of the 6th TNM edition is that reclassification of patients with nodal stage pN1 (5th edition) are now graded in the new nodal categories pN1, pN2 or pN3 according to the number and the localization of lymph node metastasis. This shifting of cases significantly increases the number of patients in UICC Stage III. Thereby, relative survival rates in the new pN categories 1, 2 and 3 and in the new UICC Stages II and III are visibly improved (so called "Will Rogers Phenomenon" or "stage migration"). Apart from that, splitting of the big group of patients with nodal stage pN1 (5th edition) provides a prognostically more meaningful stratification of patients, permitting easier identification of prognostically unfavorable cases. A new division of cases also resulted for patients with nodal stage pN2 (5th edition) according to the number of affected lymph nodes, permitting a better identification of prognostically more favorable cases in this group. Conclusion: Prognostic data that relate to the 5th edition of TNM and the tumor stages defined therein are not directly comparable with the 6th edition of TNM. This should be considered when analyzing clinical studies using the new staging system.