Risk factors for ovarian cancer in Taiwan: a case-control study in a low-incidence population.

Objective: We conducted a case-control study to identify risk factors for ovarian cancer in Taiwan, a low-incidence population where the incidence has been on the rise.
Methods: Cases were 86 women (age range 20-75, median 47) drawn from patients with primary, invasive epithelial ovarian cancer diagnosed between 1993 and 1998 in the Taipei metropolitan area, with the following histologic subtypes: 35% serous, 27% mucinous, 21% endometrioid, 15% clear cell, and 2% unspecified adenocarcinoma. Controls were 369 women (age range 20-75, median 44) selected from patients who were hospitalized at the same time for treatment of unrelated diseases. Subjects were interviewed in person regarding sociodemographic and reproductive characteristics, family and medical history, and diet.
Results: A strong inverse relationship of ovarian cancer to each live birth was observed (odds ratio (OR) = 0.43, 95% confidence interval (CI) = 0.20-0.89; OR = 0.30, 95% CI = 0.13-0.69; and OR = 0.18, 95% CI = 0.05-0.62 for parity of 1 or 2, 3-5, and >5, respectively). Menopause was associated with increased risk of disease (OR = 2.15, 95% CI = 1.21-3.83). A trend toward protection was seen with breastfeeding for more than 1 year (OR = 0.55, 95% CI = 0.29-1.01). No dietary factor was associated with an increased disease risk. Milk intake was associated with a decreased disease risk (OR = 0.45, 95% CI = 0.28-0.74).
Conclusion: The strong protective effect of parity was supported by this study, and the decline in parity is likely an important reason for the rising incidence of ovarian cancer in Taiwan. A decreased disease risk was also seen with milk intake. In addition, the difference in the distribution of histologic subtypes in this population compared with high-incidence populations may point to further differences in risk factors.