結腸鏡檢查減少大腸直腸癌風險 但只限左側

作者：Zosia Chustecka  
出處：WebMD醫學新聞

　　December 30, 2009 — 另一篇以社區為基礎的結腸鏡篩檢研究顯示，它的確降低了大腸直腸癌風險，但是僅限於左側的大腸直腸癌，而非右側。
　　
　　這個最新發現來自德國一個有3,287名研究對象的研究，其結果線上發表於12月30日的美國國家癌症研究院期刊(Journal of the National Cancer Institute)。
　　
　　過去10年間，曾接受過結腸鏡檢查的586名研究對象中，36人(6.1%)在結腸鏡檢時發現末期大腸直腸癌，未曾接受過結腸鏡檢查的2,701名研究對象中，308人(11.4%)在結腸鏡檢時發現末期大腸直腸癌。
　　
　　德國海德堡德國癌症研究中心的Hermann Brenner醫師等研究者認為，此一風險降低是明顯的。
　　
　　然而，研究者指出，此風險降低僅限於左側末期腫瘤，而非右側。之前的結腸鏡檢查，與左側大腸與直腸的末期腫瘤形成風險降低 67%有關，但是右側大腸並未有風險降低。
　　
　　他們指出，不過，因為多數的大腸與直腸腫瘤都位於左側，我們觀察到大腸直腸癌與末期腺瘤的整體風險明顯降低。
　　
　　【和之前的研究相當一致】
　　加拿大安大略省多倫多市Sunnybrook健康科學中心、Odette癌症中心的Linda Rabeneck醫師與St.Michael's醫院的NancyBaxter博士等編輯認為，這些結果與最近發表的一些研究相當一致，都顯示結腸鏡檢查對於降低大腸直腸癌發生率和死亡率有整體效果，但是在近端和遠端癌症的效果有顯著差異。
　　
　　他們指出，此研究的重要貢獻是，觀察到讓我們瞭解結腸鏡檢查之效果的證據。
　　
　　編輯們也指出，觀察到的證據可以用於解釋結腸鏡檢如何有效降低人們發生大腸直腸癌的問題，而明確的答案需等待隨機試驗之結果，目前有一個隨機試驗(the Northern European Initiative on ColorectalCancer)正在進行中，預計要到2026年才會有結果。
　　
　　他們認為，同時，觀察型證據持續增加，這個問題的答案變得較不確定 。
　　
　　【右側大腸癌有何不同？】
　　研究者表示，此研究的限制之一是，在任何位置發現的末期腫瘤數不多，不過，左側大腸與直腸各部位的風險降低模式一致，右側大腸各部位則無風險降低，他們指出，這個與部位有關的發現也和許多之前的研究相當一致。
　　
　　他們認為，透過加強內視鏡操作者的訓練、加強確保品質的方法、發展提升右側結腸檢查的技術等，或許可以克服右側結腸沒有效果的問題。
　　
　　他們接著表示，不過，因為右側結腸的癌症可能性低，使它未被納入藉由生物基礎及早偵測的考量，如果其他研究可以顯示出其可能性，那麼，乙狀結腸鏡和結腸鏡檢查對於早期偵測和預防大腸直腸癌的相對價值就須被再度評估。
　　
　　Rabeneck醫師與Baxter博士在編輯評論中指出，有充分證據顯示結腸鏡檢查對於近端結腸的效果比遠端結腸差，但是他們也指出，關於此差異的原因還不清楚。
　　
　　編輯們接著表示，或許是因為生物上的差異而限制了結腸鏡檢查對於近端結腸的效果，右側結腸腺瘤一般比左側病灶較平坦些，因此，比較難發現和移除。
　　
　　編輯們指出，本研究和其他研究發現的結腸鏡檢查對於預防近端結腸之大腸直腸癌的限制，引起了相當重要的問題：相較於軟式乙狀結腸鏡，結腸鏡對於大腸直腸癌篩檢是否有額外助益？此外，如果有額外利益，是否大到足以和大眾使用結腸鏡檢查的額外風險與花費取得平衡。
　　
　　德國Ambulatory健康照護研究中心部份資助該研究。研究作者與編輯皆宣告沒有相關財務關係。
　　
　　J Natl Cancer Inst. 線上發表於2009年12月30日。


Colonoscopy Reduces Colorectal Cancer Risk But Only on Left Side

By Zosia Chustecka
Medscape Medical News

December 30, 2009 — Another study of colonoscopy screening in thecommunity setting has shown that it does reduce the risk for colorectalcancer, but this reduction is seen only for left-sided, notright-sided, colorectal cancer.

The latest findings come from Germany, from a study of 3287 participants, and are published online December 30 in the Journal of the National Cancer Institute.

Advanced colorectal cancer was detected by colonoscopy in 36 (6.1%) of586 participants who had undergone a previous colonoscopy in thepreceding 10 years vs 308 (11.4%) of 2701 participants with no previouscolonoscopy.

This is a "substantial risk reduction," comment the study authors,headed by Hermann Brenner, MD, MPH, from the German Cancer ResearchCenter in Heidelberg, Germany.

However, the risk reduction was seen only in left-sided advancedneoplasms and not right-sided ones, the researchers point out. Aprevious colonoscopy was associated with a 67% reduced risk foradvanced neoplasia in the left side of the colon and the rectum, but norisk reduction was seen in the right side of the colon.

"However, because most neoplasms in the colon and rectum are located onthe left side, substantial overall risk reduction for colorectalcancers and advanced adenomas was observed," they add.

"Remarkably Consistent" With Previous Studies

These results are "remarkably consistent with a number of recentlypublished studies, all of which demonstrate the overall effectivenessof colonoscopy for reduction of colorectal cancer incidence andmortality but with a marked variance in effectiveness for proximal anddistal cancers," comment editorialists Nancy Baxter, MD, PhD, from St.Michael's Hospital, Toronto, Ontario, Canada, and Linda Rabeneck, MD,MPH, from the Odette Cancer Center, Sunnybrook Health Sciences Centre,Toronto, Ontario, Canada.

They add that the study is an important contribution to theobservational evidence that "must inform our understanding of theeffectiveness of colonoscopy."

The editorialists also point out that observational evidence is allthat is available at present to address the question of how effectivecolonoscopy is at reducing the burden of colorectal cancer in thepopulation. A definitive answer can come only from a randomized trial,and although one is underway (the Northern European Initiative onColorectal Cancer), outcome data are not expected until 2026.

In the meantime, as the observational evidence continues to mount, theanswer to this question becomes less certain, they suggest.

Is Right-Sided Colon Cancer Different?

One of the limitations of this study was the small number of advancedneoplasms found at any location, the researchers comment."Nevertheless, consistent patterns of risk reduction in all parts ofthe left colon and rectum were observed, with absence of risk reductionin all parts of the right colon," they add. These site-specificfindings are also "remarkably consistent" with several previousstudies, they note.

"Possibly, the lack of effect in the right colon could be overcome tosome extent by enhanced training of endoscopists, by enhanced measuresof quality assurance, and by development of technology that enhancesinspection of the right colon," they suggest.

"Nevertheless, the possibility that cancer in the right colon simplydoes not lend itself equally well to early detection on biologicalgrounds has to be considered," they continue. "If this possibilitycould be demonstrated in other investigations, then the relative meritsof sigmoidoscopy and colonoscopy in the early detection and preventionof colorectal cancer would need to be re-evaluated."

Compelling evidence that colonoscopy is a less effective tool in the proximal colon than [the] distal colon

In their editorial, Drs. Baxter and Rabeneck add that there is"compelling evidence that colonoscopy is a less effective tool in theproximal colon than [the] distal colon," but they also add that the"underlying reasons for the differential performance are unclear."

"There may be biological differences that limit the potentialeffectiveness of colonoscopy in the proximal colon," the editorialistscontinue. "Right-sided colonic adenomas tend to be flatter thanleft-sided lesions and are, therefore, harder to identify and remove."

The potential limitations of colonoscopy for preventing colorectalcancer in the proximal part of the colon — as identified in this andother studies — raises very important questions, the editorialistsnote. Is there an incremental benefit of colonoscopy vs flexiblesigmoidoscopy for colorectal cancer screening? Also, if there is anincremental benefit, is it large enough to justify the additional risksand cost of colonoscopy for screening in the population, they ask.

The study was supported in part by a grant from the Central ResearchInstitute of Ambulatory Health Care in Germany. The study authors andeditorialists have disclosed no relevant financial relationships.