The TNM system is the most widely used means for classifying the extent of cancer spread. TNM Classification of Malignant Tumours, Sixth Edition provides the new, internationally agreed-upon standards to describe and categorize cancer stages and progression. Published in affiliation with the International Union Against Cancer (UICC), this pocket guide contains important new and updated organ-specific classifications that oncologists and other professionals who treat patients with cancer must use (starting with cases diagnosed and treated in 2003) to adequately classify tumours for prognosis and treatment. The revised standards include: Major alterations in the classifications concerning carcinomas of the liver, biliary tract and pancreas, pleural mesothelioma, bone tumours, malignant melanoma of the skin, ophthalmic tumours, and the regional lymph node classification of breast carcinoma; a nasal cavity tumour classification; changes in classification of head and neck tumours; risk factors for gestational trophoblastic tumours that have been modified according to FIGO recommendations; new subcategories in gastric, prostate, and kidney tumour classifications and in the stage grouping of colorectal carcinoma; schemes for recording the assessment of sentinel lymph nodes and isolated tumour cells. The definition of the y symbol for cases classified during or after initial multimodality therapy has been further clarified. These changes will enhance the value of TNM in treatment planning and as a prognostic indicator.