To investigate the clinicopathological characteristics of patients treated with additional surgery after non-curative endoscopic resection for Tis colorectal cancer and estimate the application value of secondary surgery.

The clinical data of 34 patients with Tis colorectal cancer who underwent additional surgery after non-curative endoscopic resection in Gastrointestinal Cancer Center of Guangdong Hospital of Traditional Chinese Medicine from January 2013 to December 2021 were retrospectively collected to analyze the characteristics of endoscopic treatment, indications of additional surgery, postoperative pathological results, and the main reason leading to additional surgery.

Among the 34 patients included, eighteen were male and 16 were female, with a median age of 58 years (range 30~78 years). The lesions were located in right-sided colon, left-sided colon and rectum in 6, 17, and 11 cases respectively. In accordance with Yamada classification, seven cases were classified as type Ⅰ, eight were type Ⅱ, seventeen were type Ⅲ and 2 were type Ⅳ. Endoscopic mucosal resection(EMR), endoscopic submucosal dissection(ESD) and endoscopic piecemeal mucosal resection(EPMR) were performed in 20, 6 and 4 patients respectively, and 4 patients were treated with snaring resection. The indications of additional surgery included suspicious submucosal invasion in 21 cases (61.8%), safety resection margin ＜1 mm in 21 cases (61.8%), positive vertical or lateral resection margin in 10 cases (29.4%) and piecemeal resection in 8 cases (23.5%). Twenty-four (70.6%) patients were diagnosed as tumor invasion of muscularis mucosa, and lymphovascular invasion or tumor budding was present in no patient. The median time between endoscopic resection and surgery was 14 days. Postoperative pathological results showed that residual tumor was present in 10 patients (29.4%) including intramucosal carcinoma 8 cases (23.5%) and T1 adenocarcinoma in 2 cases (5.9%). The median number of total retrieved lymph nodes was 12 (range 3~34), and there was no patient confirmed lymph node metastasis. The risk factors for residual tumor included positive resection margin and piecemeal resection.

The ambiguous pathological diagnosis after endoscopic resection is the main reason leading to additional surgery for Tis CRC. The risk of submucosal invasion might be overestimated in Tis CRC when making surgical decisions. As a result, the oncological benefit of surgical treatment was limit for Tis CRC patients with surgical indications and endoscopic surveillance might be a safer strategy.