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结肠癌探秘(续3)

(2009-11-29 10:05:53)
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How can colon cancer be prevented?

 Unfortunately, colon cancers can be well advanced before they are detected. The most effective prevention of colon cancer is early detection and removal of precancerous colon polyps before they turn cancerous. Even in cases where cancer has already developed, early detection still significantly improves the chances of a cure by surgically removing the cancer before the disease spreads to other organs. Multiple world health organizations have suggested general screening guidelines.

Digital rectal examination and stool occult blood testing

It is recommended that all individuals over the age of 40 have yearly digital examinations of the rectum and their stool tested for hidden or "occult" blood. During digital examination of the rectum, the doctor inserts a gloved finger into the rectum to feel for abnormal growths. Stool samples can be obtained to test for occult blood (see below). The prostate gland can be examined at the same time.

An important screening test for colorectal cancers and polyps is the stool occult blood test. Tumors of the colon and rectum tend to bleed slowly into the stool. The small amount of blood mixed into the stool is usually not visible to the naked eye. The commonly used stool occult blood tests rely on chemical color conversions to detect microscopic amounts of blood. These tests are both convenient and inexpensive. A small amount of stool sample is smeared on a special card for occult blood testing. Usually, three consecutive stool cards are collected. A person who tests positive for stool occult blood has a 30% to 45% chance of having a colon polyp and a 3% to 5% chance of having a colon cancer. Colon cancers found under these circumstances tend to be early and have a better long-term prognosis.

It is important to remember that having stool tested positive for occult blood does not necessarily mean the person has colon cancer. Many other conditions can cause occult blood in the stool. However, patients with a positive stool occult blood should undergo further uations involving barium enema x-rays, colonoscopies, and other tests to exclude colon cancer, and to explain the source of the bleeding. It is also important to realize that stool which has tested negative for occult blood does not mean the absence of colorectal cancer or polyps. Even under ideal testing conditions, at least 20% of colon cancers can be missed by stool occult blood screening. Many patients with colon polyps are tested negative for stool occult blood. In patients suspected of having colon tumors, and in those with high risk factors for developing colorectal polyps and cancer, flexible sigmoidoscopies or screening colonoscopies are performed even if the stool occult blood tests are negative.

Flexible sigmoidoscopy and colonoscopy

Beginning at age 50, a flexible sigmoidoscopy screening tests is recommended every three to five years. Flexible sigmoidoscopy is an exam of the rectum and the lower colon using a viewing tube (a short version of colonoscopy). Recent studies have shown that the use of screening flexible sigmoidoscopy can reduce mortality from colon cancer. This is a result of the detection of polyps or early cancers in people with no symptoms. If a polyp or cancer is found, a complete colonoscopy is recommended. The majority of colon polyps can be completely removed by colonoscopy without open surgery. Recently doctors are recommending screening colonoscopies instead of screening flexible sigmoidoscopies for healthy individuals starting at ages 50-55. Please read the Colon Cancer Screening article.

Patients with a high risk of developing colorectal cancer may undergo colonoscopies starting at earlier ages than 50. For example, patients with family history of colon cancer are recommended to start screening colonoscopies at an age 10 years before the earliest colon caner diagnosed in a first-degree relative, or five years earlier than the earliest precancerous colon polyp discovered in a first-degree relative. Patients with hereditary colon cancer syndromes such as FAP, AFAP, HNPCC, and MYH are recommended to begin colonoscopies early. The recommendations differ depending on the genetic defect, for example in FAP; colonoscopies may begin during teenage years to look for the development of colon polyps. Patients with a prior history of polyps or colon cancer may also undergo colonoscopies to exclude recurrence. Patients with a long history (greater than 10 years) of chronic ulcerative colitis have an increased risk of colon cancer, and should have regular colonoscopies to look for precancerous changes in the colon lining.

Genetic counseling and testing

Blood tests are now available to test for FAP, AFAP, MYH, and HNPCC hereditary colon cancer syndromes. Families with multiple members having colon cancers, members with multiple colon polyps, members having cancers at young ages, and having other cancers such as cancers of the ureters, uterus, duodenum, etc., should be referred for genetic counseling followed possibly by genetic testing. Genetic testing without prior counseling is discouraged because of the extensive family education that is involved and the complicated nature of interpreting the test results.

The advantages of genetic counseling followed by genetic testing include: (1) identifying family members at high risk of developing colon cancer to begin colonoscopies early; (2) identifying high risk members so that screening may begin to prevent other cancers such as ultrasound tests for uterine cancer, urine examinations for ureter cancer, and upper endoscopies for stomach and duodenal cancers; and (3) alleviating concern for members who test negative for the hereditary genetic defects.

Diet and colon cancer to prevent colon cancer

People can change their eating habits by reducing fat intake and increasing fiber (roughage) in their diet. Major sources of fat are meat, eggs, dairy products, salad dressings, and oils used in cooking. Fiber is the insoluble, nondigestible part of plant material present in fruits, vegetables, and whole-grain breads and cereals. It is postulated that high fiber in the diet leads to the creation of bulky stools which can rid the intestines of potential carcinogens. In addition, fiber leads to the more rapid transit of fecal material through the intestine, thus allowing less time for a potential carcinogen to react with the intestinal lining. For additional information, please read the Colon Cancer Prevention article.

http://www.medicinenet.com/colon_cancer/page5.htm

 

翻译:大连翻译职业学院英语学院07英日1班  赵阳

结肠癌该如何预防?

不幸的是,在结肠癌被检测到时,其癌症病情已经迅速地发展了。预防结肠癌的最有效的方法就是对病情在早期就能够发现并在发生癌变之前就对结肠息肉做出切除。即使有时在发现癌症时病情已在发展,但在癌症病情转移到体内其它器官之前对其进行手术切除也会大大增加治疗成功的几率。多个世界健康组织建议本着总体筛查原则进行治疗。

直肠指检及粪便潜血检测

原则上建议每个人在40岁以后每年都进行一次直肠指检及粪便潜血检测,来检测隐藏或"藏匿"的血液。在直肠指检过程中,医生会用戴着手套的手指插入到患者直肠来感觉是否有异常增长。粪便样本,可用来测试潜血(见下文)。与此同时前列腺也可以接受检查。一个重要的大肠癌和息肉的筛查检查就是粪便潜血试验。结肠或直肠肿瘤往往会流血,且血液会慢慢进入粪便。粪便中参杂的少量血液仅凭肉眼是无法看到的。常用的大便潜血试验的方法就是依靠化学色素转化来检测微量血液。这些检查既方便又便宜。在一种特殊卡上涂上少量粪便样本用于潜血检查。通常情况下,需要连续三次收集粪便卡。一个经粪便潜血检测检查过的人会有30%至45%呈阳性息肉,3%至5%呈阳性结肠癌。在这种情况下发现的癌症往往是早期的癌症,并且会有更好的远期预后。

需要注意的一点是,在粪便潜血检测中结果呈阳性并不一定意味着此人一定患有结肠癌。许多其他条件可能会导致有潜血出现在粪便中。然而,粪便潜血呈阳性的患者也应作进一步的病情评估,这涉及钡灌肠X光检查,结肠镜检查,和其他检查,以排除结肠癌,并搞清楚出血来源。同样重要的一点是要认识到,粪便潜血化验结果呈阴性也并不意味着没有大肠癌或息肉。即使是在理想的检测环境下,也至少有20%的结肠癌在粪便潜血检查过程中被漏诊。许多患者的粪便潜血检测结果呈阴性,但却患有结肠息肉。对于有些怀疑患有结肠癌的患者,和有些具有患大肠息肉和大肠癌高风险的人们来说,即使粪便潜血检测结果呈阴性,灵活的乙状结肠检查或者筛选性的结肠镜检查也要被实施。

灵活的乙状结肠镜和结肠镜检查

一个人从50岁起,原则上建议三年或五年需要进行一次灵活的乙状结肠镜筛检。灵活的乙状结肠检查是通过一个可视管道对直肠和降结肠进行的一种检查。(结肠镜检查的一种短型检查)。最近的研究表明,使用灵活的乙状结肠镜检查可降低结肠癌的死亡率。这是由于检测的息肉或早期癌症的患者并没有什么症状。如果息肉或癌症被发现,医生就会建议患者进行一次完整的大肠镜检查。大多数结肠息肉可以在结肠镜检查过程中完全被切除,而无需经过开放手术。最近医生建议50岁至55岁的健康人群应采用筛选性的结肠镜来进行身体检查,而最好不要采用灵活的乙状结肠镜检查。请阅读直肠癌筛查有关文章。

可能患上大肠癌的高风险患者应该早从50岁起就进行结肠镜的检查。例如,有结肠癌家族病史的患者应在其第一直系亲属被诊断为结肠癌的最早期的10年前就进行结肠镜的筛查,或比其第一直系亲属癌前结肠息肉被确诊的5年前就进行检查。有遗传性结肠癌的症状患者,其症状如家族性腺瘤性息肉, AFAP , HNPCC ,和MYH等,都被建议及早开始结肠镜检查。这些建议因基因缺陷而有所不同,例如,在FAP中;结肠镜检查可在青少年时期就被应用来寻找是否有结肠息肉的产生。先前有息肉或结肠癌病史的患者也应经结肠镜检查,以排除复发的可能。而长期患有慢性溃疡性结肠炎的患者(多于10年),会有更大的结肠癌患病风险,应定期接受结肠镜检查,来检查结肠壁的癌前变化。

遗传咨询和检测

血液化验,现已是测定FAP, AFAP , MYH ,与HNPCC等遗传性大肠癌综合征的方法。对于有多个结肠癌患者的家庭,成员多患有结肠息肉,年纪轻轻就患上癌症,并可能患上其他癌症,如输尿管癌,子宫癌,十二指肠癌等,对于他们来说,在有可能通过基因测试之后应提交遗传咨询的一些材料。没有预先进行咨询的基因测试是不值得提倡的,因为这与家庭教育程度有关,而且涉及到解读检查结果的复杂性。

在遗传测试之后进行遗传咨询的优势包括:( 1 )确定那些结肠癌患病几率高的家庭成员,并使他们尽早进行结肠镜的检查;( 2 )确定高风险的成员,以便可以开始检查,以防止其他癌症的发生,如利用超声波测试子宫癌,通过尿液检查输尿管癌和用上层的内镜检查胃和十二指肠癌;和( 3 )减轻那些遗传缺陷检查结果呈阴性的患者的忧虑。

饮食和结肠癌,防止结肠癌

人们可以在他们的饮食过程中改变自己的饮食习惯,减少脂肪摄入量和增加纤维(粗粮)。脂肪的主要来源是肉类,蛋类,乳制品,沙拉酱,和用于烹饪油。纤维是不可溶解的,植物材料的一部分,在水果当中呈现的植物不能被人体消化的部分,蔬菜和全麦面包和谷物。以下是一种假定,即饮食中的高纤维导致人体排出大量粪便,以此可以消除肠道内的潜在致癌物质,那么,就要减少潜在致癌物质对肠道内壁进行反应的时间。如需详细资讯,请阅读预防结肠癌相关文章。

 

 

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