Malignant recurrence and distal metastasis after complete local resection of colorectal "high-grade intraepithelial neoplasia": incidence and risk factors.

BACKGROUND: Colorectal high-grade intraepithelial neoplasia is defined as a high-grade neoplastic lesion with no invasion of submucosa. Because pathological evaluation has inevitable sampling errors, invasive cancer may be underdiagnosed as high-grade intraepithelial neoplasia by regarding submucosa invasion as an indispensable criterion for malignancy. This study was to evaluate the reliability of colorectal "high-grade intraepithelial neoplasia" diagnosis and identify predictive factors of underdiagnosis.

METHODS: Colorectal high-grade intraepithelial neoplasia patients treated with complete local excision were followed up. Clinicopathologic features were compared between cases with malignant recurrence or distal metastasis and those without.

RESULTS: Of 491 lesions reviewed, 13 (2.6 %) developed local malignant recurrence or distal metastasis, which were statistically significantly associated with rectal location (p = 0.047), sessile growth (p = 0.002), large diameter (p = 0.005), villous adenoma (p = 0.00), transanal local resection (p = 0.001), and piecemeal specimens (p = 0.009). Of the 13 cases, 11 were located in the rectum, including 10 in the low position (<=6 cm from the anal verge, mean 3.6 cm). Deeper pathological examination was performed on the paraffin-embedded tissue blocks of the 13 primary tumors and revealed no evidence of submucosa invasion.

CONCLUSION: The diagnosis of colorectal high-grade intraepithelial neoplasia based on local resection is relatively reliable. However, regarding invasion of submucosa as an indispensable criterion for malignancy may contribute to the choice of overly conservative treatment, especially in the situation that the radical resection requires removing the anus.