Objectives To describe baseline characteristics of Lynch syndrome(LS) patients enrolled in a prospective study of annual surveillance versus risk-reducing surgery(RRS) and determine prevalent cases of endometrial intraepithelial neoplasia(EIN), endometrial(EC) and ovarian(OC) cancers

Methods A prospective cohort study was implemented in February 2015 for LS patients diagnosed based on a pathogenic variant in mismatch repair genes but unaffected by gynecologic cancer. Baseline investigations included CA-125, ultrasound and endometrial biopsy(EMB); further investigations were performed as warranted. Patients were recommended RRS by age 40 or following child-bearing. All others had annual surveillance and analyzed per treatment received.

Results Among 82 patients, 41 underwent RRS and 41 annual surveillance. The most frequent mutation was MSH6(34.1%). 25.9% had a personal history of LS-associated cancer and 97.5% had a family history, most commonly being colorectal(74.4%). Patients in the RRS group had a higher median age at LS diagnosis(47 vs 32 years, p<0.001) and entry into LS screening program(47 vs 33 years, p<0.001). At baseline, median CA-125 was 10 in both groups(p=0.65). The baseline EMB rate was 85%(n=70) with an abnormality rate of 4.88% (two EIN in surveillance group and one EC in RRS group). Seventy(91%) individuals underwent baseline ultrasound and no OCs were detected. In patients undergoing RRS, the median time from initial visit to surgery was 6.1 months(range 1.1–20.7); 3 additional EINs were diagnosed on final pathology.

Conclusions In LS patients followed in a surveillance program, the prevalent rate of EIN/EC is 5–10%, mostly in the RRS group. RRS within the recommended time prevents diagnosis of significant pathology.