Wednesday, May 23, 2012

Is Flexible Sigmoidoscopy Good Enough Against Colon Cancer?

Sadly but also ironically, singer Robin Gibb died earlier this week from colon cancer, just one day before a randomized trial published online in the New England Journal of Medicine concluded that screening flexible sigmoidoscopy was associated with decreases in both colon cancer incidence & mortality.  Like the announcement regarding mass screening for prostate cancer by the US Preventive Services Task Force on the same day, this study is similar in that it goes against the grain and is an affront to conventional wisdom.  Kind of like Columbus proving the world isn't flat.

Why do I say this?  Well, flexible sigmoidoscopy at its best only evaluates the distal (last) third of the your colon, the descending portion from about the splenic flexure onwards.  It ignores the proximal ascending colon as well as the transverse colon in that it doesn't have the same reach.  Furthermore, the prep for the procedure is nothing at all like the arduous bowel cleansing required for colonoscopy.  So if your bowel isn't cleaned out from the top down but rather just a simple enema, and we only look at a portion of the colon, the procedure can't be good enough, right?  Conventional wisdom compares flexible sigmoidoscopy to performing mammograms on just one breast when the patient has two.

So how did the authors arrive at their conclusion?  They randomized 154, 900 men & women 55-74yo to either active intervention or usual care.  The former consisted of baseline flexible sigmoidoscopy followed by repeat procedure in 3-5yrs.  After almost 12yrs, the rate of colon cancer in those actively screened by flexible sigmoidoscopy was 21% lower than those randomized to usual care.  More specifically, there was a 29% reduction in distal colon cancers (as expected) along w/surprising 14% reduction in proximal colon cancers.  Most importantly, there was a 26% reduction in colon cancer mortality, due in no small part to a 50% reduction in death from distal colorectal cancers (again as expected).

What's the take message?  Something is better than nothing, just like a bird in the hand is worth two in the bush.  Sure, colonoscopy preceded by complete bowel prep & cleansing is theoretically better in many different aspects than flexible sigmoidoscopy preceded by an enema.  But if patients are not willing to undergo the more involved procedure, what good is it for the general population?  Don't forget that checking stool for blood is actually a bit late since you're hoping that the colon cancer announces its presence by bleeding whereas the two invasive procedures actively search for benign polyps to remove prior to morphing into adenomas and then adenocarcinomas.  The difference between the two is how much territory is analyzed.  But as of this week, it appears for now that the flexible sigmoidoscopy is good enough in the battle against colon cancer.  As for mammograms, I'm still going to recommend screening both breasts until a peer-reviewed article demonstrates otherwise.



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