Screening of Large Bowel Cancer




When large bowel cancers are detected early and accurately, they are curable.



緩下剤 laxative;偽性ペルオキシダーゼ pseudoperoxidase activity;グアヤク脂 guaiac;穿孔 perforation;腺腫 adenoma;大腸癌 large bowel cancer;大腸内視鏡検査 colonoscopic examination;大便 feces;非ステロイド性抗炎症薬 nonsteroidal anti-inflammatory drug;便潜血検査 stool occult blood test;ポリープ切除術 polypectomy



Screening for large bowel cancers are performed to detect them at earlier, more curable stages and allow the patients to be cured of the diseases. 



credit:  colonic polyp  WEO


It takes a long latent period after development of adenoma development until occurrence of subsequent cancer, on the order of 10 to 20 years.  Thus, colonoscopic examination and polypectomy can prevent patients from having large bowel cancers.



As individuals age, the morbidity of large bowel cancers tends to rise.  Most individuals need to start screening for large bowel cancer at age 50.



In Japan, there are two types of screening for large bowel cancer: stool occult blood test and colonoscopic examination. 



Although stool occult blood tests may simply detect some advanced cancers (and some advanced adenomas), colonoscopic examination can detect both cancers and adenomas.



These test and examination may be used alone or in combination.



In Japanese official screening for large bowel cancers, individuals who are aged 50 or older and who apply for the national health insurance can annually undergo fecal occult blood tests at a very low examination fee less than 1,000 yen (US $10).  In this screening, precancerous polyps cannot be detected and resected.  However, most Japanese medical institutions screen patients using colonoscopic examination instead of fecal occult blood tests.  As a result, polyps can be resected so as to prevent the patients from having large bowel cancers.  When patients who apply for the national health insurance undergo colonoscopic examination, their fees may be 10,000 yen (US $ 100) to 30,000 yen (US $300) depending on whether they use sedative and undergo polypectomy.    


Tumors of large bowel cancer bleed.  The blood is contained in feces.  

Fecal occult blood tests detect hemoglobin in the blood. 



Fecal occult blood tests are guaiac based.  The guaiac tests detect blood in stool through the pseudoperoxidase activity of hemoglobin.



Fecal occult blood tests are performed with two samples of feces collected in two successive days. 



The results of fecal occult blood tests are affected by medications (such as aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs)), animal and fish meats, and some vegetables (those containing iron and vitamin C) that individuals take.  Thus, individuals who undergo fecal occult blood tests need to avoid these substances so that they do not affect the results of the fecal occult blood tests.



Individuals need to annually undergo fecal occult blood tests.  If test results are positive, the individuals need to undergo colonoscopic examination as soon as possible. 



Since colonoscopic examination can detect neoplasia that occurs in the large bowel as well as resect adenoma, it can be prevented from developing cancers.   



Before individuals have colonoscopic examination, they need to use a laxative to empty the large bowel.  This examination may be done under sedation.  The examination should be performed by physicians sufficiently trained and experienced in colonoscopy and polypectomy.  Otherwise, individuals who undergo colonoscopic examination may have complications such as perforation.



Colonoscopic examination is commonly used in most of Japanese medical institutions. 



Colonoscopic examination and polypectomy have allowed cancer incidence of individuals to decrease at a higher rate.



If no adenomas are found in the initial screening colonoscopic examination, the next colonoscopic examination can be performed at an interval of 10 years.