癌症是以异常细胞生长为特征的众多疾病的统称，这些异常细胞会失控地分裂，并能浸润和毁坏正常身体组织。癌症通常可以扩散到全身各处。

选择某些生活方式会增加患癌风险。抽烟、女性每天饮酒超过一杯、男性每天饮酒两杯以上、过度暴露在阳光下或经常晒伤起疱、肥胖和不安全的性行为都可能导致癌症。

Some different solutions have already been investigated and proven being ineffective but nonetheless keep on being marketed and promoted. Most cancers researcher Andrew J. Vickers said, "The label 'unproven' is inappropriate for these kinds of therapies; it is actually time to say a large number of substitute most cancers therapies have been 'disproven'."[204]

Radiation therapy is Employed in about half of circumstances. The radiation might be both from interior resources (brachytherapy) or exterior sources. The radiation is mostly very low Vitality X-rays for managing skin cancers, although increased Strength X-rays are useful for cancers throughout the system.[193] Radiation is often made use of Along with surgical treatment and/or chemotherapy.

Most cancers diagnosis might cause psychological distress and psychosocial interventions, which include chatting therapy, may assist individuals with this.

筛查旨在确认尚未出现症状但已具有暗示特定癌症或癌症前期迹象的个体。如在筛查中发现异常，则应进行进一步检测以作出明确诊断，如果证明存在癌症，还应转诊进行治疗。

Individuals with most cancers have a heightened danger of blood clots in their veins that may be lifetime-threatening.[210] The usage of blood thinners like heparin decrease the potential risk of blood clots but haven't been demonstrated to raise survival in people with most cancers.[210] Individuals that get blood thinners even have a heightened hazard of bleeding.[210]

筛查规划仅对某些类型而非所有类型的癌症有效，而且一般来说，筛查规划比早期诊断复杂得多并需要更大量的资源，包括需要特殊设备和专门人员。即使建立了筛查规划，早期诊断规划也依然必要，以便查明那些发生在不符合筛查的年龄或风险因素标准的人群中的癌症病例。

The Dutch professor Francois de la Boe Sylvius, a follower of Descartes, believed that all sickness was the result of chemical procedures and that acidic lymph fluid was the reason for cancer. His modern 癌症 Nicolaes Tulp thought that most cancers was a poison that slowly spreads and concluded that it was contagious.[230]

畸胎瘤是性腺或胚胎剩件中的全能细胞发生的肿瘤，常发生于性腺，一般含有两个以上胚层的成分，结构混乱，也有良性和恶性之分。

一些最常见的癌症类型，如乳腺癌、宫颈癌、口腔癌和结肠直肠癌等，如能早期发现并根据最佳做法进行治疗，治愈概率很高。

Human immunodeficiency virus (HIV) does in a roundabout way cause most cancers however it brings about immune deficiency that could magnify the chance as a consequence of other infections, from time to time approximately numerous thousandfold (in the case of Kaposi's sarcoma). Importantly, vaccination against the hepatitis B virus and also the human papillomavirus have been proven to almost get rid of the chance of cancers brought on by these viruses in individuals effectively vaccinated ahead of an infection.

準確的癌症分期與診斷對於癌症的治療相當重要，癌症治療的原則是先確立治療目標，主要目標則可分為治癒癌症、延長生命、減輕痛苦及安寧療護四大類，常見的治療方式有以下幾項。

手术治疗主要用于去除瘤灶，达到治疗的目的，同时也适用于癌症的预防、诊断、 分期、术后结构重建与功能康复等。这种方法不存在生物抵抗性；无潜在致癌可能； 不受肿瘤差异性影响；能提供准确的病理分期及组织学类型；适用于大部分未扩散 的肿瘤。但是会破坏正常组织；可有手术并发症，可致畸形、影响正常功能，甚至 危及生命；已有转移者，不能完全治愈；重要器官无法彻底切除。