Which type of colonic polyp is associated with the highest risk of malignancy?

Villous adenomas are considered to be associated with the highest risk of malignancy among colonic polyps. These neoplastic lesions are characterized by a greater propensity for anaplasia and can undergo malignant transformation. The size of villous adenomas is also significant, as larger polyps are more likely to harbor carcinoma; typically, those over 2 centimeters have an increased risk.

In contrast, other polyp types carry much lower risks of developing into cancer. Hyperplastic polyps, for example, are generally non-neoplastic and have a minimal risk of progression to malignancy. Juvenile polyps, while they may be associated with colorectal cancer in specific syndromic contexts, are mostly benign and have a low malignant potential in the general population. Inflammatory polyps are most often the result of conditions like inflammatory bowel disease and do not have the same risk for malignant transformation as villous adenomas.

Thus, the distinct pathological characteristics and behavior of villous adenomas delineate them as the polyp type with the greatest association with colorectal cancer risk.