Undetermined Margins After Colonoscopic Polypectomy for Malignant Polyps: The Need for Radical Resection

Discussion

In our study, the incidence of residual cancer was 18%, and the incidence of stage III disease was 10.0% in patients who underwent curative resection after colonoscopic polypectomy. Undetermined margins were the most common indication for further radical surgery, and 26.1% of patients with undetermined margins were found to have residual cancer.

In another study, with similar indications for further radical surgery, the incidence of residual cancer was reported to be about 2-11% (2, 5, 6), which is lower than that in our study. The incidence of locoregional lymph node metastasis was also higher in our study (10%) than in other studies (4-7%) (2, 5, 6).

Regarding the indications for further radical surgery after endoscopic procedure for malignant colorectal polyp, most published reports suggest positive margin at polypectomy, poorly differentiated histological type, deep submucosal invasion, and the presence of lymphovascular invasion (2, 5, 7-11). These are high-risk factors for residual tumor, lymph node metastasis, and recurrence (3-5).

T1 cancer has been associated with regional lymph node metastasis in 7-15% of patients (5, 8, 12, 13). Kudo divided the depth of submucosal invasion of sessile polyps into: Sm1, invasion within the upper third of the submucosa (<300 μm from the muscularis mucosa); Sm3, with more than two-thirds of the submucosa invaded; and Sm2, intermediate level (14). The degree of submucosal invasion is a risk factor for lymph node metastasis in CRC, in particular for Sm3 (6, 12). Other studies reported that the risk of lymph node metastasis was 1-3% in Sm1, 8% in Sm2, and 23% in Sm3 cancer (6, 12). Based on these data, additional radical resection is recommended for Sm2 and Sm3 lesions of CRC after polypectomy (6, 16). Our results show why radical resection is needed for Sm2 lesions. Case 6 in Table IV had an Sm2 lesion with clear resection margin after polypectomy. Further colorectal resection was performed because of Sm2 invasion. In the final pathological report, tumor deposit was found without residual tumor in the colonic wall, and finally, this was T1N1cM0, stage III. This patient received adjuvant chemotherapy with FOLFOX regimen, and is alive without recurrence or metastasis.

The treatment for patients with undetermined margins is not yet established (5). In many articles on endoscopic treatment for malignant colorectal polyp, undetermined margins, or unknown margins were not analyzed in detail, and were only mentioned briefly (2, 5). Butte et al. suggested that an unknown margin status could be considered with positive or close resection margins because the inability to evaluate the margin is associated with piecemeal resection or poor specimen orientation (2). Piecemeal polypectomy for malignant polyp is considered as incomplete resection and is a risk factor for residual cancer; therefore, further excision or surgical resection is required (6, 15, 17, 18). Boenicke et al. mentioned that snare polypectomy of malignant polyps could be effective and safe but polypectomy artifacts make it difficult for pathologists to evaluate the resection margin of sessile polyps (5, 11).

In several studies on colonoscopic polypectomy, the incomplete resection rate was reported to be about 4.1-20.2% (17, 19). This incompleteness of removal is related to piecemeal resection and poor ability of endoscopy (17, 19). Pathological reports of incomplete resection could be presented as positive resection margins or unknown margins. Incomplete resection may be related to poor ability of endoscopy (17, 19). Undetermined margins could be evidence of piecemeal polypectomy (2, 11, 17, 20). In our study, an undetermined margin status was chiefly reported in polypectomy specimens obtained from outside clinics

Interestingly, compared to other indications for further radical surgery, the group with undetermined margins had higher incidence of residual cancer and lymph node metastasis. Undetermined margins could also be a negative factor for lymph node metastasis (5). In other words, overlooking the undetermined margin is a type of undertreatment, and causes locoregional recurrence and distant metastasis in the long-term follow-up.

Considering that the incidence of absence of residual tumor is almost 82%, few surgeons have been concerned that further radical resection might be overtreatment (21). However, even their study, they obtained unassessable resection margins after a colonoscopic procedure in 40% of the patients and residual cancer in 30% (21). Therefore, we should measure the oncologicaI benefit for the 20% of patients with residual cancer and operation-related risk for the 80% of patients without residual cancer. With the development of surgical technique and instruments, operation-related mortality and complication rates are decreasing remarkably (6). Benizri et al. reported that the severe surgical complication rate (Dindo-Clavien classification grade III-V) was 12.5% in patients who underwent radical colorectal surgery after colonoscopic polypectomy, with complications including intra-abdominal abscess, wound hematoma, anastomotic leakage, pulmonary embolism, myocardial infarction, and hemoperitoneum (6). However, in our study, there were no severe complications, although minor complications (Dindo-Clavien classification grade I-II) were reported, including atelectasis, wound infection, and ileus. For an experienced surgeon, oncological benefit is an important issue compared to operation-related risks.

There is a limitation to our retrospective study due to the rather small sample size. Only patients who underwent colonoscopic polypectomy followed by radical colorectal resection were enrolled in the study. Most polypectomies were performed at outside clinics, and only representative slides were reviewed at our Hospital.

In summary, undetermined margins after an endoscopic procedure for malignant colorectal polyp are reported commonly. Patients with undetermined resection margins had a higher incidence of residual tumor and lymph node metastasis. Therefore, an accurate assessment of the resection margins after colonoscopic polypectomy is important for deciding the treatment plan, and awareness of the clinical significance of undetermined margins could avoid undertreatment of colorectal cancer.

In conclusion, undetermined resection margins after colonoscopic polypectomy could be considered as an additional indication for further radical colorectal surgery. This factor could be helpful in improving the oncological outcome of CRC.