Histologic risk factors and clinical outcome in colorectal malignant polyp: a pooled-data analysis.

PURPOSE The malignant polyp carries a significant risk of lymphohematic metastasis and mortality. Clinical usefulness of histologic risk factors is still controversial. The study was designed to compute the association between the main histologic risk factors and the occurrence of unfavorable outcomes in patients with malignant polyps. METHODS A MEDLINE search regarding malignant polyps was performed. Three histologic risk factors (positive resection margin, poor differentiation of carcinoma, vascular invasion) and five (residual disease, recurrent disease, lymph node metastasis, hematogenous metastasis, mortality) unfavorable clinical outcomes were evaluated. Further analysis was performed by subgrouping polyps in high-risk and low-risk groups. RESULTS Thirty-one studies enrolling 1,900 patients with malignant polyp were selected. Positivity of resection margin was significantly predictive of the presence of residual disease (odds ratio, 22; P < 0.0001), poorly differentiated carcinoma was associated with an increased mortality (odds ratio, 9.2; P < 0.05), and vascular invasion with a higher lymph node metastasis risk (odds ratio, 7; P < 0.05). Patients with high-risk polyps showed a significantly worse outcome than those with low-risk, especially for mortality (odds ratio, 11; P < 0.05). Surgical-related death was as low as 0.8 percent. CONCLUSIONS All three histologic risk factors are significantly associated with the clinical outcome. Classification in low-risk and high-risk patients may be regarded as a meaningful staging procedure.