Reappraisal of the characteristics, management, and prognosis of intramucosal colorectal cancers and their comparison with T1 carcinomas.

Background And Aims: The recent description of "invasive" forms of intramucosal carcinoma (IMC) has rekindled interest in studying the characteristics, management, and prognosis of IMCs and comparing them with T1 colorectal cancers (CRCs).

Methods: This population-based study included 282 cases of IMC and 207 cases of T1 CRC diagnosed by colonoscopy after a positive fecal blood test through a screening program.

Results: IMC presented mainly in the form of pedunculated polyps (68.4%) located in the distal colon (69.9%) ≥20 mm in size (60.6%). IMCs were resected endoscopically in 227 (80.5%) patients and surgically resected in 55 (19.5%) patients. Surgical patients had more right-sided, more sessile, and larger lesions. There was no sign of lymphovascular invasion. Compared with T1 CRCs, IMCs demonstrated lower rates of sessile polyps (31.6% vs 49.8%, P < .0001), primary and ultimate surgical treatment (19.5% vs 39.1% and 19.9% vs 78.7%, P < .0001, respectively), lymph node metastasis in surgical patients (0% vs 9.5%, P = .041), cancer recurrence and cancer-related mortality (0% vs 5.6% and 0% vs 2.5%, respectively), and bleeding after endoscopic resection (1.8% vs 8.7%, P = .001). By multivariate analysis of the pooled cohort (IMC + T1 CRC, n = 489), the factors significantly associated with first-line surgery were shown to be polyp characteristics and the gastroenterologist who performed the colonoscopy.

Conclusions: IMCs account for a quarter of all screening-detected CRCs. They have an excellent prognosis regardless of whether endoscopic or surgical treatment is performed. IMCs differ significantly from T1 carcinomas in terms of management and prognosis.