By EMMA ROSS, AP Medical Writer
LONDON (AP) - Women infected with the common sexually transmitted human papilloma virus have a higher risk of developing cervical cancer if they have taken birth control pills
Experts say the study supports what many gynecologists have long suspected -- that there is a causal connection between the pills and cervical cancer.
Previous studies have not ruled out the possibility women who take the pill may simply be more likely to be infected with human papilloma virus, the main cause of the cancer.
"This study suggests that if you've got an HPV infection, oral contraceptives may actually be promoting the rate at which that progresses to cancer," said Dr. Jack Cuzick, head of mathematics, statistics and epidemiology at Cancer Research UK in London. He was not connected with the study.
Nearly all sexually active women will be infected by HPV sometime during their lives, but in most cases the immune system quickly eliminates it.
The key issue is why, in some cases, the virus does not go away. If the infection persists, the chances of cancer increase enormously.
The study was conducted by the International Agency for Research on Cancer, an arm of the World Health Organization.
Researchers pooled data from eight earlier studies of 3,769 women from four continents. Of those, 1,853 had cervical cancer, and 1,916 did not.
As expected, nearly all the women with cancer tested positive for HPV, while hardly any who were cancer-free had the virus.
The WHO researchers found that women who had taken the pill were no more likely than the others to be carriers of HPV.
However, those infected with HPV who had used birth control pills
The increased risk persisted for up to 14 years after stopping the contraceptives.
Women who had taken the pill for 10 years or more were four times more likely to get the disease than those who had never taken it.
Using the pill for less than five years did not result in a higher chance of cervical cancer.
Cuzick said the findings should be interpreted cautiously because the women were only tested for the virus once.
"Ideally, they should be positive on two occasions, at least six months apart, before you call them positive," he said.
The research was to be published Wednesday on the Web site of The Lancet medical journal.
Women have about a 1 percent chance of developing cervical cancer. Based on the new findings, taking the pill for five years or more could push that chance up to about 3 percent and taking it for a total of 10 years could raise it to about 4 percent.
Worldwide, almost 360,000 women were diagnosed with cervical cancer in 1990, the latest date for which figures are available. Of those, 190,000 died of the disease. It is the second most common cancer in women.
Cervical cancer strikes 12,900 American women each year and kills 4,400 of them.