恶性肿瘤(cancer)
肿瘤的一类，有时不严格地称为癌症。是身体组织的异常细胞发生不受控制的、与周围组织不相协调的增生所形成。无完整包膜，细胞分化程度低。某些瘤细胞早期还能完成一定的功能，但随病情进展，其外观、结构及功能日益异常。恶性肿瘤可浸润周围组织或通过淋巴管、血管、体内腔管转移到远隔部位形成新病灶。肿瘤细胞最常从淋巴管转移。恶性肿瘤也可以程度来区分，有时还保留该器官组织特有的细胞特徵。无论是发展的阶段或程度，都会影响到存活率。激素、病毒、吸烟、节食和辐射线都可能引起恶性肿瘤。恶性肿瘤几乎可发生於任何组织中，包括了血液（参阅leukemia）和淋巴液（参阅lymphoma）。早期诊断和治疗增加了治癒的机会，治疗方式包括了化学疗法、手术、放射疗法。参阅breast cancer、carcinogen、Kaposi's sarcoma、laryngeal cancer、lung cancer和skin cancer。
English version：
cancer
Uncontrolled multiplication of abnormal cells. Cancerous cells and tissues have abnormal growth rates, shapes and sizes, and functioning. Cancer may progress from a localized tumor (confined to the site of origin) to direct extension (spread into nearby tissue or lymph nodes) and metastasis (spread to more distant sites via the blood or lymphatic system). This malignant growth pattern distinguishes cancerous tumors from benign ones. Cancer is also classified by grade, the extent to which cell characteristics remain specific to their tissue of origin. Both stage and grade affect the chances of survival. Genetic factors and immune status affect susceptibility. Triggers include hormones, viruses, smoking, diet, and radiation. Cancer can begin in almost any tissue, including blood (see leukemia) and lymph (see lymphoma). When it metastasizes, it remains a cancer of its tissue of origin. Early diagnosis and treatment increase the chance of cure. Treatment may include chemotherapy, surgery, and radiation therapy. See also breast cancer, carcinogen, Kaposi's sarcoma, laryngeal cancer, lung cancer, skin cancer.