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。
在正常细胞生长期间经常会发生基因突变。但细胞含有一种可识别何时发生错误并修复错误的机制。有时会漏掉某种错误。这种情况可能导致细胞癌变。
現代人工作忙碌，飲食習慣差，多為外食、重口味並常延遲用餐，加上生活壓力大、熬夜、作息不穩定，以及長期久坐、缺乏運動等，這些不良生活習慣都會增加罹癌風險。
癌症有超過一百個種類，一般可依據癌細胞原發部位來分類，例如肺癌、乳癌等；另外能根據不同組織或細胞做以下分類：
[188] The effectiveness of chemotherapy is commonly constrained by its toxicity to other tissues in the body. Even though chemotherapy doesn't give a everlasting remedy, it might be helpful to lower signs or symptoms which include discomfort or to lessen the dimensions of the inoperable tumor during the hope that medical procedures will come to be doable Later on.[citation necessary]
The most typical kinds of cancer vary, but the cancer load seems at the very least as higher in pets as in individuals. Animals, usually rodents, will often be Employed in most cancers investigate and research of pure cancers in bigger animals may well advantage exploration into human most cancers.[272]
Predicting brief- or lengthy-phrase survival depends upon numerous factors. The most crucial will be the most cancers form along with the affected person's age and General health. Those who are frail with other health problems have decreased survival charges than usually healthful individuals. Centenarians are not likely to survive for five years even when procedure is profitable.
多數癌症是自發性的（英语：sporadic），但是有些癌症還是與遺傳有關，通常遺傳到缺陷的腫瘤抑制基因時會有較顯著的影響和症狀。舉例而言：
Big-scale mutations entail the deletion or get of the percentage of a chromosome. 癌症 Genomic amplification occurs each time a mobile gains copies (normally 20 or even more) of a small chromosomal locus, typically that contains one or more oncogenes and adjacent genetic content. Translocation happens when two separate chromosomal locations come to be abnormally fused, generally in a attribute spot.
出生后发生的基因突变。大多数基因突变会在您出生后发生，并且不会被遗传。有多种因素会导致基因突变，例如抽烟、辐射、病毒、致癌化学物质（致癌物）、肥胖症、激素、慢性发炎和缺乏运动。
Some slow-increasing cancers are significantly typical, but usually are certainly not lethal. Autopsy studies in Europe and Asia confirmed that up to 36% of people have undiagnosed and seemingly harmless thyroid most cancers at some time in their deaths and that 80% of Males create prostate most cancers by age eighty.
dans le but de protéger les espèces menacés, mais beaucoup font encore l’objet de capture et dressage pour amuser les touristes ou fabriquer des souvenirs.
最近幾十年的研究中，最為確定的發現就是抽煙和癌症間密切的相關性，許多流行病學研究也已經證實這樣的關係。根據美國的數據顯示，隨著吸煙人數增加，肺癌的死亡率急劇升高。隨著近年來廣為宣導抽菸對身體的傷害之後，抽菸人口的減少，也反映在肺癌死亡率降低上。
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