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 criteria 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 depends on the physical examination, laboratory findings, and imaging studies. Pathologic stage is determined following surgical exploration of disease spread and histological examination of tissue. The TNM classification system has evolved over 50 years to accommodate increasing knowledge about cancer biology. Efforts are ongoing to keep the system both synchronized with the most sophisticated cancer technology and simple for ease of clinician/patient use. Upcoming molecular technologies, such as genomic and proteomic profiling of tumors, microRNA profiling, and even ex vivo living tumor tissue treatment, could improve the current TNM staging system. This chapter describes the current TNM system using breast, lung, ovarian, and prostate cancer examples.