Fewer years of ovulation mean less risk of ovarian cancer
Pitt researchers try to figure out why
Years of research have shown that the less time a woman spends ovulating during her lifetime, the lower the risk of ovarian cancer. What’s not known is why.
A new study by a University of Pittsburgh professor and other researchers looked at the ovulation histories of more than 47,000 women worldwide to try to figure out an answer.
“If we understand how a disease arises, that will help us to devise prevention strategies,” said Francesmary Modugno, a Pitt professor and an investigator at the MageeWomens Research Institute and UPMC Hillman Cancer Center. “For ovarian cancer, prevention is extremely important because it’s a highly fatal disease.”
Pitt researchers Zhuxuan Fu and Maria Mori Brooks also contributed to the study, along with dozens of other researchers around the world.
Through the Ovarian Cancer Association Consortium, a group formed in 2005, researchers gained access to 25 studies that had already been conducted on ovulation and ovarian cancer. Those studies included 26,204 control subjects and 21,267 cases of women with ovarian cancer.
The researchers calculated years of ovulation by taking the total years between menstruation and menopause and subtracting out time not spent ovulating because of oral contraceptive use, pregnancy and breastfeeding. The study found that for every year spent ovulating, the risk of developing ovarian cancer increased by 4% — a figure in line with previous research.
But the study also examined how each method of ovulation suppression affected risk, and whether there was a difference between women whose ovulation was affected by the pill, pregnancy or breastfeeding, and those who just naturally spent fewer years ovulating.
“We wanted to understand, is it really because they suppress ovulation or is there something else going on?” said Modugno.
The study found that, indeed, there is something else going on.
Taking oral contraceptives, being pregnant, or breastfeeding all reduce the number of years spent ovulating and provide significant protection against ovarian cancer. However, the impact of each of these factors differed from what would be expected if suppressing ovulation alone were how they impart protection. The impact of taking oral contraceptives was four times what was expected, while that of pregnancy and breastfeeding were substantially greater.
“If all ovulations are equal, two women who had the same total ovulatory years would have the same risk, and that’s not what we found,” said Modugno.
The researchers were also able to separate out different types of ovarian cancers and examine the relationship between years of ovulation.
Surprisingly, they found that one type of ovarian cancer, mucinous tumors, was not associated with years of ovulation, while four other types were.
The findings about the subtypes of ovarian cancer “will hopefully open the door to basic scientists doing model and cell culture work” for further investigation, Modugno said.
There is also, of course, plenty of room for more research on the preventive effects of ovulation.
“It tells us that there’s something going on with these behaviors women have that afford protection, but we currently don’t know what this is,” she said. “What this paper tells us is what it’s not.”