Increased risk of breast cancer in women with uterine myoma: a nationwide, population-based, case-control study

OBJECTIVE To evaluate if uterine myoma is associated with breast cancer. METHODS This case-control study used a nationwide database in Taiwan. We identified 24,315 patients with newly diagnosed breast cancer as cases and matched them with 24,281 patients without breast cancer on age, sex, urbanization, income, and initial diagnosis date. Patients with prior mastectomy were excluded. We used logistic regression analysis to assess the association between uterine myoma and breast cancer while adjusting for confounders. We evaluated the impact of surgical removal of uterine myoma on subsequent breast cancer among patients with uterine myoma. RESULTS We found that 2,892 (11.9%) patients with newly diagnosed breast cancer and 2,541 (10.5%) patients without breast cancer had a history of uterine myoma. The association between breast cancer and uterine myoma was significant (adjusted odds ratio [aOR]=1.14; 95% confidence interval [CI]=1.07-1.21; p<0.001). This association remained in patients who used hormone (aOR=1.20; 95% CI=1.08-1.33; p=0.001) or who did not use hormone (aOR=1.11; 95% CI=1.03-1.19; p=0.005) within 5 years prior to the index date. Surgical removal of uterine myoma was not associated with a decreased risk of breast cancer (aOR=0.99; 95% CI=0.88-1.10; p=0.795). CONCLUSION A minor increased risk of breast cancer was found in women with a history of uterine myoma. This association remained in patients with recent hormone use. Removal of uterine myoma was not associated with decreased risk of breast cancer.