Adenomas found on colonoscopy significantly associated with incidence of colorectal cancer

By Robyn Boyle, RPh, for MDLinx
Published June 11, 2018

Key Takeaways

A new study published in JAMA showed that patients with an advanced adenoma found during colonoscopy had a significantly increased risk of developing colorectal cancer (CRC) compared with those with no adenoma.

Benjamin Click, MD, from the University of Pittsburgh, Pittsburgh, PA, led the post hoc analysis from a prospective cohort study of participants in the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial of positive flexible sigmoidoscopy (FSG) to evaluate the relationship between adenomas found and the risk of CRC.

The multicenter trial enrolled 154,900 men and women aged 55 to 74 years who were randomized to receive FSG at baseline and again at year 3 or 5 vs usual care. Participants who had a positive FSG result (finding of a polyp or mass) were referred to their primary care physicians for follow-up. Approximately 75% of these patients underwent colonoscopy.

Information regarding polyp size, number, and histology was obtained from medical records; specimens were not reviewed centrally. The number, size, and histologic characteristics of lesions detected at the colonoscopy were qualified as advanced adenoma (≥ 1 cm, high-grade dysplasia, or with tubulovillous or villous histology); nonadvanced adenoma (< 1 cm without advanced histology); or no adenoma.

Lesions in the rectum through the splenic flexure were defined as distal, and those in the transverse colon to the cecum were defined as proximal.

Baseline demographics such as age and body mass index were recorded, as were risk factors known to influence risk of colon cancer. These included smoking status, gender, race, family history of cancer(s), and history of aspirin or ibuprofen use.

The primary outcome was CRC incidence, and the secondary outcome was CRC mortality.

A total 15,935 participants underwent colonoscopy. Most were men (59.7%) and white (90.7%), and the median age was 64 years. On initial colonoscopy, 2,882 participants (18.1%) had an advanced adenoma, 5,068 participants (31.8%) had a nonadvanced adenoma, and 7,985 participants (50.1%) had no adenoma; the median follow-up for CRC incidence was 12.9 years.

The incidence rates of CRC per 10,000 person-years of observation were 20.0 (n=70), 9.1 (n=55), and 7.0 (n=71) for advanced adenoma, nonadvanced adenoma, no adenoma, respectively.

Participants with an advanced adenoma were significantly more likely to develop CRC when compared with participants with no adenoma (rate ratio [RR]: 2.7; P < 0.001).

Compared with the no adenoma group, participants with one to two nonadvanced adenoma(s) had an 8.2% higher frequency of subsequent colonoscopy (78.1% for the nonadvanced adenoma group vs 69.9% for the no adenoma group, P=0.001).

There was no significant difference in CRC risk between participants with nonadvanced adenoma when compared with no adenoma (RR: 1.2; P=0.30). Compared with participants with no adenoma, those with advanced adenoma were at significantly increased risk of death due to CRC (RR: 2.6; P=0.01), but mortality risk in participants with nonadvanced adenoma was not significantly different (RR: 1.2; P=0.68).

The authors acknowledge that the study had a number of limitations. The colonoscopy examination was prompted by a positive FSG result, so participants may not be representative of individuals with a negative initial colonoscopy result. Information on previous examinations was not available, so some adenomas might have been removed before enrollment, and colonoscopy protocols were not standardized.

In addition, information regarding the quality of colonoscopy was limited. Pathology was not centrally reviewed, endoscopic procedures and pathologic assessments were performed from 1993 to 2006, and may be different than current techniques. The study was a post hoc analysis with limited statistical power.

“Over a median of 13 years of follow-up, participants with an advanced adenoma at diagnostic colonoscopy prompted by a positive screening flexible sigmoidoscopy result were at significantly increased risk of developing colorectal cancer compared with those with no adenoma,” concluded the authors.

They added: “Identification of nonadvanced adenoma may not be associated with increased colorectal cancer risk.”

To read more about this study, click here.

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