Objective Ovarian clear cell carcinoma has unique clinical and molecular features compared with other epithelial ovarian cancer histologies. Our objective was to describe the incidence of second primary malignancy in patients with ovarian clear cell carcinoma.

Methods Retrospective cohort study of patients with ovarian clear cell carcinoma at two tertiary academic centers in Toronto, Canada between May 1995 and June 2017. Demographic, histopathologic, treatment, and survival details were obtained from chart review and a provincial cancer registry. We excluded patients with histologies other than pure ovarian clear cell carcinoma (such as mixed clear cell histology), and those who did not have their post-operative follow-up at these institutions.

Results Of 209 patients with ovarian clear cell carcinoma, 54 patients developed a second primary malignancy (25.8%), of whom six developed two second primary malignancies. Second primary malignancies included: breast (13), skin (9), gastrointestinal tract (9), other gynecologic malignancies (8), thyroid (6), lymphoma (3), head and neck (4), urologic (4), and lung (4). Eighteen second primary malignancies occurred before the index ovarian clear cell carcinoma, 35 after ovarian clear cell carcinoma, and 7 were diagnosed concurrently. Two patients with second primary malignancies were diagnosed with Lynch syndrome. Smoking and radiation therapy were associated with an increased risk of second primary malignancy on multivariable analysis (OR 3.69, 95% CI 1.54 to 9.07, p=0.004; OR 4.39, 95% CI 1.88 to 10.6, p=0.0008, respectively). However, for patients developing second primary malignancies after ovarian clear cell carcinoma, radiation therapy was not found to be a significant risk factor (p=0.17). There was no significant difference in progression-free survival (p=0.85) or overall survival (p=0.38) between those with second primary malignancy and those without.

Conclusion Patients with ovarian clear cell carcinoma are at increased risk of second primary malignancies, most frequently non-Lynch related. A subset of patients with ovarian clear cell carcinoma may harbor mutations rendering them susceptible to second primary malignancies. Our results may have implications for counseling and consideration for second primary malignancy screening.