The most appropriate colon cancer screening strategy is colonoscopy beginning now. This patient's family history is consistent with hereditary nonpolyposis colorectal cancer (HNPCC). The Amsterdam II criteria include (1) three or more relatives with an HNPCC–associated cancer (including colorectal, endometrial, ovarian, urothelial, gastric, brain, small bowel, hepatobiliary, or skin), (2) two successive generations of relatives affected, (3) one affected relative a first-degree relative to two other affected relatives, and (4) one cancer diagnosed before age 50 years. Patients with HNPCC should undergo genetic counseling, and an attempt should be made to ascertain the genetic cause of cancer in the patient and family. Surveillance colonoscopy is indicated in patients who meet the clinical criteria for HNPCC, have Lynch syndrome (defined by the presence of a germline genetic mutation), or are at risk for Lynch syndrome and have not had genetic testing. The recommended surveillance interval for colonoscopy screening in patients who have or are at risk for Lynch syndrome is every 1 to 2 years beginning at age 25 years, or 2 to 5 years earlier than the youngest age at diagnosis of colorectal cancer if the affected relative was younger than 25 years old.

Colonoscopy every 5 years beginning at age 40 years (or 10 years before the earliest case in the immediate family) is the surveillance recommendation for a patient with either colorectal cancer or adenomatous polyps in a first-degree relative before age 60 years or colorectal cancer in two or more first-degree relatives at any age.

Colonoscopy every 10 years beginning at age 40 years is the U.S. Multi-Society Task Force on Colorectal Cancer recommendation for a patient with either colorectal cancer or adenomatous polyps in a first-degree relative aged 60 years or older or colorectal cancer in two second-degree relatives with colorectal cancer at any age.

Although the earliest colorectal cancer diagnosis in this patient's family was at age 47 years, she should begin screening now owing to her increased risk related to her family history consistent with HNPCC.

A 5-year interval beginning at age 50 years is not recommended for patients who have or who are at risk for Lynch syndrome; it would be appropriate for low-risk patients diagnosed with one to two tubular adenomas smaller than 10 mm.