Aberrant crypt foci (ACF) are abnormal clusters of colonic glands in the lining of the large intestine. They have been linked to the early stages of colon cancer development and are often monitored in individuals at high risk for the disease. Synonyms for ACF include colonic microadenomas, precancerous lesions, dysplastic crypts, and abnormal crypt foci. These terms all refer to abnormal growths in the colon that may progress to cancer if left untreated. It is important for individuals with a family history of colon cancer or other risk factors to undergo regular screening for ACF and other precancerous conditions of the colon.