An abnormal lump may be harmless or life-threatening. A tumor is an abnormal mass of tissue that forms when cells grow and divide excessively or fail to die on schedule.

Benign tumors remain localized and usually grow slowly; malignant tumors invade nearby tissue and may metastasize. The word neoplasm is often used interchangeably. Symptoms depend on location and size—compression, bleeding, hormone production, or systemic effects. Imaging and biopsy establish the nature of the mass.

Not every tumor requires aggressive treatment; some are observed. Others need surgery, radiation, drugs, or combinations. Accurate classification by histology and, increasingly, molecular features guides therapy and prognosis. Early detection of malignant tumors generally improves outcomes.

• Abnormal mass of tissue from uncontrolled cell growth
• May be benign or malignant
• Diagnosed by imaging and tissue examination
• Management ranges from observation to multimodal therapy