767P - Ovarian cancer risk factors in relation to family history

Background

Women with a family history of breast and/or ovarian cancer have an increased risk of ovarian cancer. Yet it remains uncertain if common ovarian cancer risk factors – especially those which can be modified - affect this high-risk population similarly to the general population.

Methods

Using the Danish and Swedish nationwide registers, we established two nested case-control study populations in women with a family history of breast and/ or ovarian cancer (2,138 ovarian cancer cases, 85,240 controls) and women without (10,730 ovarian cancer cases, 429,200 controls). The overall and histology-specific associations between ovarian cancer risk and common ovarian cancer risk factors were assessed with conditional logistic regression. The country-specific estimates were then combined based on a fixed-effect assumption.

Results

Multiparity, hysterectomy, tubal ligation, salpingectomy, and oral contraceptive (OC) use were associated with a reduced risk of ovarian cancer in both women with and without a family history, while endometriosis and menopausal hormone treatment (MHT) were associated with increased risk. Similar histology-specific associations were also found for this two groups of women: multiparity and OC use were shown with protective effects across all the histologic subtypes except mucinous ovarian cancer, risk of which was not associated with OC use; MHT was linked to an increased risk of serous ovarian cancer but a decreased risk of the mucinous and clear cell cancers; Endometriosis correlated particularly to an increased risk of endometrioid and clear cell ovarian cancer.

Conclusions

This is the largest study to date on ovarian cancer risk in relation to family history of breast and/or ovarian cancer. Existing knowledge on ovarian cancer protective factors can be considered equally valid when considering women with a family history of ovarian/breast cancer. Given the higher baseline risk for women with a family history, special attention should be paid to risk factors like endometriosis and nulliparity in this high-risk population.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Mermaid project (Mermaid III).

Disclosure

All authors have declared no conflicts of interest.