In a study of more than 2,000 women aged 20 to 69, investigators found that those with a history of endometriosis, ovarian cysts, or overactive thyroid were at increased risk for ovarian cancer. Talc use, which may spur inflammation in the ovarian lining, also elevated cancer risk. A team led by Roberta B. Ness, of the Graduate School of Public Health, reports the findings in the March issue of Epidemiology.
Certain factors that suppress ovulation and hormones that affect the ovaries -- such as pregnancy, birth control pill use, and breastfeeding -- have widely been found to protect against ovarian cancer. Yet the risk related to ovarian inflammation is less well understood, according to Ness and her colleagues. Inflammation, they note, produces toxic oxidants that inflict genetic damage in cells, a process that may lead to cell changes and cancer.
In interviews with women with and without ovarian cancer, the study authors found that, as expected, pregnancy and breastfeeding reduced cancer risk. In addition, the team found a 50% decrease in risk with a first pregnancy and small dips with each subsequent pregnancy. Oral contraceptives also lowered cancer risk when used for at least one year.
The Pittsburgh researchers then questioned the women on factors that can trigger ovarian inflammation. Three medical conditions were found to increase cancer risk, relative to women without the conditions: ovarian cysts, growths on the ovaries that can be harmless or dangerous, increased cancer risk by 30%; a 70% higher risk was linked to endometriosis, a condition in which pieces of the uterine lining grow outside of the uterus; and hyperthyroidism, a disorder marked by overproduction of thyroid hormones, was linked to an 80% higher risk of ovarian cancer.
Both endometriosis and ovarian cysts may trigger local inflammation, and both have been linked to ovarian cancer in previous studies, Ness and colleagues note. This study is the first, however, to connect hyperthyroidism and ovarian cancer. Hyperthyroidism, the researchers explain, often results from the immune system`s assault on the thyroid gland; such autoimmune diseases are systemic and can trigger widespread inflammation.
As in numerous other studies, women who used talc anywhere on their bodies or in their underwear showed an elevated cancer risk, even when risk factors such as family history of ovarian cancer were considered.
One condition that causes ovarian inflammation, pelvic inflammatory disease, was linked to only a slight incline in cancer risk. Other studies, the authors note, have shown a stronger link.
Having had a hysterectomy or a tubal ligation helped protect women from ovarian cancer. These procedures, the researchers explain, cut off the path between the lower and upper genital tract, blocking inflammatory substances from gaining access to the ovarian lining.
SOURCE: Epidemiology 2000;11:111-117.