2020-08-21
What Is the Meaning of a Cancer Latency Period?
癌症的潜伏期是什么意思？
Updated October 19, 2018
It can take many years between an exposure and the later development of cancer. You may have heard about people being exposed to asbestos and developing mesothelioma many years later. The case is similar when it comes to cigarette smoking and lung cancer. What this means is that there is an elapsed period of time called a latency period between exposure to a cancer-causing substance and the first signs of cancer. Why is the latency period important and how does it make determining the causes of cancer difficult? What might this mean for people who have been exposed to toxic chemicals, such as the workers involved in rescue and recovery after the World Trade Center tragedy?
从接触致癌物开始到发展成癌症，需多年时间，例如接触了石棉后，过了很多年患上间皮瘤；吸烟和肺癌也是同样道理。从致癌物暴露到癌症最早体征出现，这段时期称为潜伏期。潜伏期为何重要？它对确定癌症成因造成什么困难？对美国世贸中心救援和灾后重建人员来说，有毒化学品暴露意味着什么？
The latency period for cancer is defined as the amount of time that elapses between the initial exposure to a carcinogen (cancer-causing substance) and the diagnosis of cancer. For example, you are probably familiar with cigarette smoking as a risk factor for lung cancer. The latency period, in this case, would be defined as the length of time between the onset of smoking, and the later development and diagnosis of lung cancer.
癌症潜伏期的定义是最早的致癌物暴露到癌症确诊之间经历了多少时间。以肺癌风险因素吸烟为例，吸第一支烟与肺癌确诊之间的时长就是潜伏期。
The latency period can vary tremendously depending on the particular cancer-causing substance being evaluated and the specific cancer or cancers it causes. The period may be short, such as with the exposure to radioactive substances in Hiroshima and Nagasaki and development of leukemia, or it may be relatively long, such as the average time between exposure to asbestos and the later development of mesothelioma. Cancer may be related to either short-term high levels of exposure or long-term low levels of exposure.
潜伏期有长有短，取决于具体致癌物及其引发的癌症。在广岛和长崎接触了放射性物质后发生白血病的潜伏期短，暴露于石棉后发展成间皮瘤的潜伏期相对较长。不管是短期高水平暴露还是长期低水平暴露，都与癌症相关。
It's helpful when talking about latency periods to first review the definition of carcinogens. Carcinogens are substances in our environment which are thought to raise the risk of developing cancer.
说起潜伏期，不得不提致癌物。致癌物是环境中会增加患癌风险的物质。
These exposures may include radiation, chemicals, ultraviolet light, and even cancer-causing viruses. Examples which you may be familiar with include asbestos, radon, tobacco smoke, and arsenic.
致癌物包括辐射、化学物质、紫外线，乃至致癌病毒。为人熟知的致癌物包括石棉、氡、烟草烟雾和砷。
Carcinogenicity is not an exact science—we do not know for certain whether an exposure will cause cancer. The International Association for Research on Cancer divides carcinogens based on the likelihood that they cause cancer. Categories include:
致癌性不是精密科学，目前尚不清楚致癌物暴露会不会致癌。国际癌症研究协会根据致癌概率划分致癌物，它们包括：
Group 1 - Carcinogenic to humans
组1：人类致癌物
Group 2A - Probably carcinogenic to humans
组2A：极可能的人类致癌物
Group 2B - Possibly carcinogenic to humans
组2B：可能的人类致癌物
Group 3 - Unclassifiable as to carcinogenicity in humans
组3：不可分类的人类致癌物
Group 4 - Probably not carcinogenic to humans.
组4：可能性极低的人类致癌物
It's also very important to point out that cancer is most often a "multifactorial disease" which develops as a result of an accumulation of mutations in cells, not as the result of a single mutation (there are some exceptions, mostly with blood-related cancers). In other words, most often a number of factors work together to either produce or prevent a cancer. That said, even when one of our cells develops mutations, most of these cells do not go on to become cancerous tumors. Our immune system is well equipped with cells that get rid of abnormal and damaged cells, but cancer cells are different.
重点是癌症通常是多因素共同作用下发生的疾病，是细胞基因突变累积的结果，单个基因突变不会致癌（有例外，主要是血癌）。即使一个细胞产生基因突变，大多数细胞也不会变成恶性肿瘤。人体免疫系统可以清除异常和受损细胞，但肿瘤细胞不一样。
An example of the multifactorial causation of cancer could be women who smoke and also have a BRCA2 gene mutation. BRCA2 is a tumor suppressor gene. You may be familiar with this "breast cancer gene" due to the awareness raised by Angelina Jolie. Less well known is that women who carry a BRCA2 mutation have double the risk of developing lung cancer if they also smoke.
多因素致癌的范例可以看看携带BRCA2突变的女烟民。BRCA2是肿瘤抑制基因。安吉莉娜朱莉提高了公众对该基因的意识。有一点鲜为人知，携带BRCA2突变的女性如果吸烟的话，肺癌风险会翻倍。
In some cases, exposures to carcinogens can be more than additive. For example, the risk of lung cancer and mesothelioma for people who are both exposed to asbestos and smoke is greater than if you simply added these risks together.
有时致癌物暴露的效应不仅仅是简单相加。例如接触石棉又吸烟的肺癌和间皮瘤风险高于二者各自的风险相加。
There are many reasons why it is important to be aware of the latency period with cancer. A common example is noted in the relationship between tobacco use and lung cancer. People may feel fine for many years—during the latency period—before it becomes clear that there is an association between smoking and several types of cancer.
癌症潜伏期意识之所以重要有很多原因。例如烟草使用和肺癌，吸了烟很多年都没事（处于潜伏期），有事的时候已经晚了，吸烟原来和几种癌症有关。
The concept of latency period can help explain why we are still uncertain about the danger of exposures to people who were involved in the clean-up efforts after 911.
目前仍不清楚在911事件后收拾残局的人们会有什么危险，因为他们可能处于潜伏期。
Another example of the importance of a latency period arises in discussions about cell phone use and brain cancer. It's been argued by some people that if cell phone use is a risk factor for brain cancer we should be seeing a significant increase in these tumors. It's important to note, however, that if tobacco smoking started and became common at the same time that cell phone use took off, we still would be wondering if tobacco could cause cancer. Obviously, smoking does cause cancer, but due to the latency period of decades, we could not have made a clear assessment of risk in the analogy. In other words, the jury is still out on the exact risk between cell phone use and cancer.
有关手机使用和脑癌的讨论中，潜伏期也很重要。人们争议手机使用是否脑癌风险因素。如果是的话，脑癌发病率应呈上升趋势。如果吸烟和手机使用在同一时间变得流行，那就还要考虑烟草产品会不会致癌。显而易见，吸烟会致癌，但由于长达数十年的潜伏期，还无法准确评估二者的风险。换言之，手机使用和癌症之间的风险尚无定论。
Understanding the latency period also helps to explain one of the reasons why it is so difficult to study causation with cancer. If we were to begin a study today looking at a particular substance, we may not have results for decades. For example, at least 40 years if the latency period of a carcinogen was 40 years. For this reason, many studies (retrospective studies) look back in time. Since these studies are not carefully thought out ahead of time (like prospective studies) there are often many questions left unanswered.
潜伏期理解也有助于解释癌症成因研究如此之难的原因。如果今天开始研究某种物质，或许要到数十年后才会有结果。例如如果致癌物潜伏期为40年，那起码要等40年。因此，很多研究是回顾性研究。由于这些研究没有预先经过慎密的思考（例如前瞻性研究），通常有很多问题都没有解答。
There are several variables that influence both the likelihood that a carcinogen may result in the development of cancer and the period of time (latency period) between exposure and the diagnosis of cancer. Some of these include:
致癌概率和潜伏期有一些影响因素，包括：
The dose or intensity of exposure.
暴露剂量或强度
The duration of exposure.
暴露时长
The particular substance (some exposures are much more likely to result in cancer than others).
具体的物质
The type of cancer that results from exposure.
致癌物暴露导致的癌症类型
Age at exposure. At some points in life, the body is more susceptible to carcinogens than at others (This may be easier to understand when compared with some infections. For example, an infection with cytomegalovirus may cause severe birth defects when contacted early in pregnancy, but only a mild syndrome with fatigue at another time). With cancer, exposure to ionizing radiation in utero is more likely to result in cancer than exposure during other periods of life. In addition, substances with a long latency period are more likely to result in cancer when the exposure occurs early in life simply because people may live long enough for the cancer to develop.
暴露于致癌物的年龄。在一些人生阶段中，身体会更容易受致癌物影响。（与感染相比看看会不会更好理解，例如在怀孕早期感染巨细胞病毒会导致严重的出生缺陷，而在别的时间感染只会有轻微症状伴随疲乏）与人生其他时期相比，子宫内电离辐射暴露致癌的概率会更大。另外，当暴露发生于人生早期，潜伏期长的致癌物致癌的概率会更大。
Gender. Men and women may vary in their susceptibility to exposure. For example, it's thought by some (but not others) that women are more likely to develop lung cancer with the same amount of tobacco exposure. For women, estrogen may also play a role in lung cancer development.
性别。对于暴露易感性，男女有别。例如，有人认为，接触等量的烟草之下，女性发生肺癌的概率会更大，雌性激素也可能会影响肺癌发展。
Genetic susceptibility. A clear example of a genetic influence on cancer development is seen in people with Down syndrome, who have an increased likelihood of developing leukemia. There are many other examples. In fact, though you may be familiar with ultraviolet light as a causative factor in melanoma, it's now thought that 55 percent of melanomas have a genetic component.
遗传易感性。关于遗传对癌症的影响，白血病发生机会更大的唐氏症患者是很好的范例。还有很多其他范例。虽然事实上紫外线是黑色素瘤的病因因素，目前有人认为55%的黑色素瘤有遗传影响。
Additional risk factors for cancer
癌症附加风险因素
Other medical conditions. Immunosuppression (an inadequately functioning immune system) whether due to medical conditions, chemotherapy, or other immune suppressive drugs, raises the chances of a carcinogen leading to the development of cancer.
其他疾病。疾病、化疗或其他免疫抑制药导致的免疫抑制（免疫力下降）会增加致癌概率。
You may have heard that people who assisted in rescue and recovery efforts after 911 have an increased risk of developing cancer. We hare now hearing people ask whether those involved in the clean-up efforts have an elevated risk of lung cancer. At this time, we simply do not know. One reason that this risk is unclear is the latency period. While blood-related cancers such as myeloma and non-Hodgkin lymphoma tend to have shorter latency periods, those of solid tumors such as lung cancer are often much longer
读者可能听说过911事件后参与救援和灾后重建的人们会有更高的患癌风险。有人问现场清理人员会不会有更高的肺癌风险。我们目前还不清楚。其中一个原因就是潜伏期。骨髓瘤和非霍奇金淋巴瘤等血癌一般会有更短的潜伏期，而肺癌等实性肿瘤的潜伏期通常会更长。
Based on studies to date, there does appear to be an excess cancer risk among these people. The only systematic study of roughly a thousand firemen and rescue workers found that seven years after the tragedy, there was a 19 percent excess risk of cancer at all sites.
根据目前的研究，这些人员的确可能会有过高的癌症风险。针对约1000名消防员和救援人员的唯一的系统性研究显示，事件发生7年后，全部地点的癌症风险都过高，高出19%。
The cancers which appear to be increased so far include prostate cancer, thyroid cancer, myeloma, and non-Hodgkin’s lymphoma. Some of the carcinogens noted in dust and debris include asbestos, silica, benzene, and polycyclic aromatic hydrocarbons. There is concern that the risk of lung cancer will be greater in the future, and understanding the concept of the latency period can help explain why we do not know more at this time.
风险增加的癌症包括前列腺癌、甲状腺癌、骨髓瘤和非霍奇金淋巴瘤。在灰尘和碎片中发现的致癌物有石棉、二氧化硅、苯及多环芳烃。有人关切肺癌风险将来会更高。由于有潜伏期，目前认识仍不多。
The latency period can vary greatly with different carcinogens, but even with a single carcinogen, there can be variations in both the latency period and the type of cancers which arise. A 2017 study looked at secondary cancers in people with acute leukemia. We know that chemotherapy—while it can sometimes cure these cancers—can also be a carcinogen which causes other cancers down the line.
不同致癌物之间，潜伏期差异会很大，即使是单一致癌物，潜伏期和发生的癌症类型也可能有差异。一项2017年研究探究急性白血病患者的继发性癌症。另外，已知化疗也会致癌。
Conducted in Argentina, the study followed people with acute leukemias or lymphomas to determine both the incidence of secondary cancers (cancers caused by cancer treatments) and the average latency period between the treatment of the original leukemia or lymphoma and the development of secondary cancer. Roughly one percent of survivors developed secondary cancer. The latency period was significantly shorter for secondary blood-related cancers than for solid tumors. The average latency period for hematologic (blood-related) cancers such as leukemias and lymphomas was 51 months but varied from 10 to 110 months. The average latency period for solid tumors was 110 months, but with this period of time ranging from 25 to 236 months.
在阿根廷进行的研究跟踪了急性白血病或淋巴瘤患者，以明确继发性癌症发病率及白血病或淋巴瘤治疗和继发性癌症之间的平均潜伏期。约1%的幸存者患上继发性癌症。与实性肿瘤相比，继发性血癌的潜伏期明显更短。白血病和淋巴瘤等血癌的平均潜伏期为51个月，具体来说，从10个月到110个月不等。实性肿瘤的平均潜伏期为110个月，具体来说，从25个月到236个月不等。
As noted above, there are many substances we are exposed to each and every day that have the potential to cause cancer. This does not mean that there is a cancer conspiracy going on, or that corporations are releasing carcinogens to make money on chemotherapy drugs down the line. We simply don't have the resources, monetary input, or time to study the carcinogenicity and possible latency period of every chemical used in commerce.
如上文所述，人类每天接触的物质中很多有可能致癌。这并不意味着有癌症阴谋，或化疗药厂靠释放致癌物赚钱。我们只是没有资源、资金或时间研究每种商品中的化学物质的致癌性及可能的潜伏期。
Until a substance has been evaluated over a significant length of time, we can't know for certain what the potential risk may be. While this thought could lead some to avoid new products and head for the hills, a little common sense and caution are likely all that is needed to keep yourself safe.
物质经过长时间评估后，才会知道其潜在风险。虽然如此，却也不必害怕使用新产品和登山，只要具备常识，了解注意事项，就能确保安全。
Protect your skin and lungs. If a product recommends wearing gloves (in the fine print) wear gloves. We know that many chemicals can be absorbed through our skin. If a product recommends using good ventilation, open windows or turn on an exhaust fan. Take the time to read material data safety sheets for all chemicals you work with.
保护皮肤和肺部。如果某个产品建议戴手套，那就戴手套。已知很多化学物质会被皮肤吸收。如果某个产品建议室内通风良好，那就打开窗户，或开排气扇。如果工作中接触化学品，务必阅读化学物质安全数据表。
If you are feeling anxious, remember again that most cancers are caused by a combination of factors, and you do have some control over many of these.
如果为此感到焦虑，请记得大多数癌症是多因素综合作用下的结果，很多因素都可以控制。
参考文献
American Cancer Society. Known and Probable Human Carcinogens. Updated 11/03/16.
Centers for Disease Control and Prevention. Minimum Latency and Types or Categories of Cancer. Revised May 1, 2013.
Felice, M., Rossi, J., Alonso, C. et al. Second Neoplasms in Children Following a Treatment for Acute Leukemia and/or Lymphoma: 29 Years of Experience in a Single Institution in Argentina. Journal of Pediatric Hematology/Oncology. 2017. 39(8):e406-e412.
Li, J., Cone, J., Kahn, A. et al. Association Between World Trade Center Exposure and Excess Cancer Risk. JAMA. 2012. 308(23):2479-2488.
Veham, V., Verma, M., and S. Mahbir. Early-life exposures to infectious agents and later cancer development. Cancer Medicine. 2015. 4(12):1908-22.
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