Tumor Staging and Grading: A Primer

Cancer staging and grading are used to predict the clinical behavior of malignancies, establish appropriate therapies, and facilitate exchange of precise information between clinicians. The internationally accepted criterion for cancer staging, the tumor-node-metastasis (TNM) system, includes: (1) tumor size and local growth (T), (2) extent of lymph node metastases (N), and (3) occurrence of distant metastases (M). Clinical stage is established before initiation of therapy and is determined by physical examination, laboratory findings, and imaging studies. Pathologic stage is determined following surgical exploration of disease and histologic examination of tissue. The TNM classification system has evolved over 70 years to accommodate increasing knowledge about cancer biology. Molecular technologies such as genomic and proteomic profiling of tumors could eventually be incorporated into the TNM staging system. This chapter describes the current TNM system using breast, lung, ovarian, and prostate cancer examples.