良性腫瘤指腫瘤細胞未發生轉移與侵入周遭組織的情形，反之則稱為惡性腫瘤，多數會影響生理功能的腫瘤都是惡性腫瘤。
世卫组织和国际癌症研究机构与包括国际原子能机构在内的其他联合国组织和伙伴合作，以便：
如果篩檢為陽性，或者是出現許多前述症狀、久未改善，就需進一步診斷，癌症診斷方式包括三大類：
治療某些白血病和淋巴瘤則需要使用高劑量的化療或全身放射治療。這樣的治療方式是先將患者原有的骨髓細胞完全破壞，避免進行骨髓細胞移植時發生排斥作用。進行骨髓移植之後，依靠患者本身的復原能力，重新進行造血功能。移植的來源除了接受親屬或配對符合的捐贈者之外，也可將病患本身的骨髓細胞以及周邊造血幹細胞（英语：peripheral blood stem cell）先取出存放待日後移植所需，稱為自體移植（英语：autologous transplantation）。
如果能早期发现和治疗病例，则可降低癌症死亡率。早期发现包括两个部分，即：早期诊断和筛查。
The most common different types of most cancers vary, but the cancer load appears at least as large in pets as in individuals. Animals, ordinarily rodents, are frequently Utilized in cancer study and reports of all-natural cancers in greater animals may well benefit exploration into human cancer.[272]
The impacted genes are divided into two broad classes. Oncogenes are genes that endorse cell development and copy. Tumor suppressor genes are genes that inhibit cell division and survival. Malignant transformation can arise through the formation of novel oncogenes, the inappropriate more than-expression of ordinary oncogenes, or from the beneath-expression or disabling of tumor suppressor 癌症 genes.
免疫療法是利用人體內的免疫機制來對抗腫瘤細胞。已經有許多對抗癌症的免疫療法在研究中。目前較有進展的就是癌症疫苗療法和單株抗體療法，而免疫細胞療法則是最近這幾年最新發展的治療技術。
Regional signs might manifest mainly because of the mass on the tumor or its ulceration. As an example, mass effects from lung most cancers can block the bronchus causing cough or pneumonia; esophageal cancer can cause narrowing with the esophagus, making it complicated or unpleasant to swallow; and colorectal most cancers may possibly result in narrowing or blockages inside the bowel, influencing bowel behaviors. Masses in breasts or testicles may develop observable lumps.
神經膠質瘤：由神經膠質細胞變化成腫瘤，神經膠質細胞也是最主要的一種腦細胞類型。
例如，如果您遗传了一种使您易患癌症的基因突变，并不意味着您一定会患癌症。可能需要有一个或多个其他基因突变才会引起癌症。当您接触某种致癌物质时，您的遗传基因突变可能使您比其他人更容易患癌症。
癌細胞擴散至距離原始腫瘤遙遠的器官及組織。此時癌細胞流竄於全身，必需借助循環全身的化學治療藥物治療。安寧照護將是治療選項之一。
Taller folks have an increased danger of cancer since they have far more cells than shorter people today. Because peak is genetically established to a significant extent, taller folks have a heritable boost in most cancers hazard.[88]
烟草使用、酒精消费、不健康饮食、缺乏身体活动和空气污染是癌症（以及其他非传染性疾病）的危险因素。