Granularly mixed laterally spreading colorectal tumors (GM-LSTs) that are located in the rectum or are larger than 4 cm should be considered to be at high risk of developing into covert submucosal invasive cancer (SMIC), and should be treated by en bloc resection, according to a retrospective analysis of patients from seven Italian centers.
GM-LSTs are 1-cm or larger nonpolypoid lesions with lateral growth. They make up 1%-6% of colorectal lesions, and are important clinically because of the possibility that they are SMICs that aren’t visibly apparent.
On the one hand, homogeneous granular-type LSTs have been found to have a very low SMIC risk (0.5%) and are candidates for piecemeal removal, while non-granular LSTs present higher risk, suggesting that en bloc resection would be an appropriate strategy. Piecemeal attempts that discover a SMIC can lead to follow-up surgery because it may not be possible to evaluate submucosal invasion at pathology. Further surgery can be particularly onerous in rectal lesions, where it can reduce quality of life.
On the other hand, granularly mixed LSTs present a conundrum: SMIC risk falls somewhere between the granular and nongranular LSTs, and they make up about 25% of laterally spreading tumors.
A deeper look
To better characterize GM-LSTs and predict which might be covert SMICs,at Humanitas University in Milan and colleagues analyzed data from 693 patients with colorectal GM-LSTs at seven Italian centers, between 2016 and 2019. The results appeared in Clinical Gastroenterology and Hepatology. Median age was 69 years, and 50.6% of patients were men.
Of patients in the study, 9.5% were found to have SMICs at histology. Of these, 62.1% occurred in lesions 4 cm or larger, and none in lesions smaller than 2 cm, and 63.6% occurred in the rectum. Overall, 24.2% of patients underwent en bloc resection.
A multivariate analysis found that lesion size was associated with risk of covert SMIC (odds ratio per mm, 1.02; 95% confidence interval, 1.0-1.03). A cutoff of 4.0 cm yielded the optimal discrimination for SMIC risk, with a 6.0% risk below that size and 14.8% above (OR, 2.32; P = .002). The researchers also considered GM-LST location in this multivariate analysis, and found a greater risk of SMIC in those located in the rectum than for those in other colonic segments (15.1% vs. 5.8%; OR, 3.08; P = .004). A logistic regression model combining size and location yielded a sensitivity of 47.0%, specificity 82.6%, and area under the curve of 0.69.
When lesions of 4 cm or greater in the rectal area were compared with nonrectal lesions less than 4 cm, the number needed to treat (NNT) to detect one covert SMIC dropped from 20 to 5.
“The 22% risk of covert SMIC for ≥4-cm rectal GM-LSTs equals the 21.4%as the highest risk for nongranular LSTs, justifying the need for an aggressive treatment, especially when considering that the unexpected finding of a covert SMIC after piecemeal resection of a rectal lesion may result in an unnecessary surgery, with major consequences for the patient. Thus, referral of these patients to a center with adequate competence in advanced resection, including [endoscopic submucosal dissection], should be recommended,” the authors wrote.
They noted that the NNT of 5 is low enough to compensate for the risk of conducting ESD instead of piecemeal endoscopic mucosal resection. Meanwhile, the NNT of 20 for smaller, nonrectal tumors puts them close to the risk category of homogeneous granular LSTs, which wouldn’t justify a more complex procedure and could instead be resected piecemeal.
For rectal lesions less than 4 cm or nonrectal lesions 4 cm or larger, SMIC risk is below 10%. In deciding which approach to take, endoscopists must weigh the low risk of surgery after discovery of an unexpected SMIC. The authors suggest use of dye or virtual chromoendoscopy for lesion characterization, along with optical magnification if available.
The study had some limitations. One is that the authors did not assess how frequently the SMIC was limited to the dominant nodule, which might affect resection strategies. Another is that the actual SMIC rate in GM-LSTs may have been underestimated: Not only were signs of overt invasion an exclusion criterion, but also patients with difficult-to-treat SMIC lesions might have been referred elsewhere.
The authors disclosed no funding source and declared that they had no relevant financial disclosures.