Truly flat or depressed colorectal polyps pose a diagnostic dilemma and are always worth a closer look. A study in JAMA may have overstated the case, however, by concluding that these polyps are quite common and carry an increased cancer risk, according to CT colonography experts.
“There were several concerns regarding the study design and its conclusions, which seemed overreaching,” said Beth McFarland, MD, chair of the American College of Radiology’s colon cancer committee. “I think the issues in the article are important to fully evaluate but should be kept in perspective with other larger studies, which followed patients longitudinally with more robust outcome metrics.”
In the JAMA study, Roy Soetikno, MD, and his colleagues at the VA Palo Alto Health System in California sought to determine the prevalence of nonpolypoid colorectal neoplasms in a population of veterans. The patients underwent screening colonoscopy and also had endoscopy with indigo carmine dye if a flat lesion was suspected.
The overall prevalence of nonpolypoid lesions was 9.35%. Broken down by subpopulation, prevalence was 6.01% in the group undergoing colon cancer screening. In the total group of 764 patients with nonpolypoid lesions, the prevalence of cancer was 0.82%. The prevalence in the screening arm was 0.32%.
Dr. Soetikno’s group concluded that in these patients, nonpolypoid lesions were “relatively common... and had a greater association with carcinoma” (JAMA 299:1027-1035, 2008).
Dr. McFarland was concerned with two aspects of the study’s design.
“This study involved an older, male VA population. It was a mixed population of patients for screening, surveillance, and symptoms. The first key question is, What is the application of these results to broader screening populations?” she said.
She also questioned the combination of lesion subtypes and cancer types into such general categories.
“There is always difficulty in terms of the terminology used. Which lesions were superficially elevated vs truly flat or depressed, which are difficult to detect, and how were these types grouped together?” she asked. “There also was some mixing of pathological terminology, combining carcinoma in situ, which most generally is referred to as high-grade dysplasia, along with true invasive cancer, which increased the overall cancer incidence.”
Dr. Soetikno responds
In an e-mail interview, Dr. Soetikno addressed the issues raised by Dr. McFarland. He said that the results in this group of patients could be extended to a larger population.
“The screening population in this study resembles male patients who routinely undergo screening colonoscopy in general practice, albeit there may be a slight increase in the prevalence of colorectal neoplasms among the veterans,” he said.
With regard to the lesion descriptors, Dr. Soetikno acknowledged that superficially elevated lesions should be distinguished from completely depressed lesions. But the latter are very rare, so the term “flat” is commonly accepted as referring to slightly elevated lesions, he said.
National Polyp Study
Dr. McFarland pointed out that the results of the JAMA study differed dramatically from the findings in the National Polyp Study, which noted that flat adenomas were not associated with a higher risk for high-grade dysplasia (Clin Gastroenterol Hepatol 2:905-911, 2004).
“So these lesions were detected and did not have increased cancer risk,” Dr. McFarland said. “The definition of flat adenomas in this study might correlate better with nonpolypoid, superficially elevated, or sessile lesions. The longitudinal National Polyp Study did not demonstrate a high interval cancer rate of these missed lesions, which would argue against poor detection of these lesions with a high cancer potential.”
Dr. Soetikno called the National Polyp Study a landmark but expressed reservations.
“At the time when the NPS was conducted, there was a belief that flat polyps did not exist in the Western population. What you don’t know or don’t believe in, you don’t seek,” he said.