ORLANDO, FLA. — Colonoscopy may be the preferred method of screening for colorectal cancer in women because many of their cancers occur in the right colon, Philip S. Schoenfeld, M.D., reported at the annual meeting of the American College of Gastroenterology.
That conclusion differs from some researchers' suggestion that low-risk women aged 50-59 years who screen negative via flexible sigmoidoscopy might not need colonoscopy because they are at low risk for colorectal cancer (CRC). These researchers have suggested that performing colonoscopies in such women might be stretching the limited endoscopic resources too thin.
The problem is that flexible sigmoidoscopy may find only about one-third of the women who have advanced neoplasia on colonoscopy, said Dr. Schoenfeld of the University of Michigan, Ann Arbor.
He reached that conclusion when he saw the results of the Colorectal Neoplasia Screening With Colonoscopy in Asymptomatic Women at Regional Navy/Army Medical Centers (CONCeRN) trial. Dr. Schoenfeld was the primary investigator in the study, which included asymptomatic women between 50 and 79 years of age referred for CRC screening and asymptomatic women 40-79 years of age with positive family history of CRC who had undergone colonoscopies at Naval medical centers.
The study excluded women who had undergone flexible sigmoidoscopy in the previous 5 years or colonoscopy or barium enema in the last 10 years or who had a history of a positive fecal occult blood test (FOBT), adenomas, iron-deficiency anemia, polyposis syndrome, inflammatory bowel disease, or hematochezia, or weight loss in the last 6 months.
Of 1,463 women who had a colonoscopy completed to the cecum, 4·9% had advanced neoplasia, including adenomas larger than 10 mm, adenomas with high-grade dysplasia, villose adenomas, or CRC. The incidence of advanced neoplasia increased with age: 3·8% in 50- to 59-year-olds, 4·9% in 60- to 69-year-olds, and 7·6% in 70- to 79-year-olds.
The investigators compared the women in the CONCeRN trial with asymptomatic men referred for CRC screening via colonoscopy from Veterans Affairs Cooperative Study 380 (N. Engl. J. Med. 2000;343:162-8). About 10% of men from that study had advanced neoplasia.
Dr. Schoenfeld and his associates estimated the diagnostic yield of flexible sigmoidoscopy by examining the proportion of patients with advanced neoplasia in the left (distal) colon. Patients also were included in the diagnostic yield of flexible sigmoidoscopy if they had small adenomas in the distal colon—which normally necessitate a colonoscopy—and then were found to have advanced neoplasia in the proximal (right) colon.
When men and women from the two trials were matched for age, negative FOBT status, and negative family history of CRC, advanced neoplasia was found in significantly more men aged 50-59 years (4·7%) and 60-69 years (10·6%) than in women aged 50-59 years (2·9%) and 60-69 years (5%). But in women, advanced neoplasia occurred significantly more often in the right than in the left colon. Flexible sigmoidoscopy would have had an estimated diagnostic yield of only 35% in these women. This is significantly less than the estimated diagnostic yield of 66% obtained by flexible sigmoidoscopy in men in the Veterans Affairs study.
If flexible sigmoidoscopy had been performed in all the women in the CONCeRN trial, advanced neoplasia would have been found in only 1·7%, and 3·2% with advanced neoplasia would have been missed, he said.
Flexible sigmoidoscopy would have missed more cases of advanced neoplasia in women than in men, despite its increased prevalence in men, because of its left-sided distribution in men, Dr. Schoenfeld added.