RESUMEN
The 7th edition of the TNM classification includes only minor changes in the main TNM categories for breast cancer. Only ductal and lobular carcinoma in situ (DCIS, LCIS), and isolated Paget's disease of the nipple are classified as pTis, but not precursor lesions such as atypical ductal or lobular hyperplasia (ADH, ALH). AJCC emphasizes that microscopic measurement is the most accurate and preferred method to determine pT in small invasive cancers and stresses the importance of strict adherence to criteria for T4 cancers. For better distinction from micrometastases in regional lymph nodes, small clusters of cells not greater than 0.2 mm, or nonconfluent or nearly confluent clusters of cells not exceeding 200 cells in a single histologic lymph node cross section are classified as isolated tumour cells (pN0(i+)). The pN classification has otherwise remained unchanged. In the setting of patients having received neoadjuvant therapy, ypT1-ypT3 is based on the total extent of viable tumour cells, irrespective of tumour regression. Stage I breast tumours have been subdivided into Stage IA and Stage IB; Stage IB includes small tumours (TI) with lymph node micrometastases (N1mi). These changes and clarifications will contribute to maintaining the clinical and prognostic relevance of TNM in breast cancer.