Sex at earlier ages may explain the higher risk of cervical cancer among poor women, according to an investigation by the International Agency for Research on Cancer in Lyon, France. Previous theories centered on lower screening rates among the poor and possibly higher prevalence of human papillomavirus (HPV), the cause of most cervical cancers. The IARC findings were based on case-control studies involving nearly 20,000 women.

The association of cancer with early sex is not just relevant for adolescents, as the risk is also higher for women who debut at age 20 rather than age 25, said lead author Dr. Silvia Franceschi.

"In our study, poorer women had become sexually active on average four years earlier," Franceschi said. "So they may have also been infected with HPV earlier, giving the virus more time to produce the long sequence of events that are needed for cancer development."

Disparities in cervical cancer prevalence between rich and poor have been noted worldwide, despite apparently similar rates of HPV infection. In the new study, researchers found a two-fold higher risk of cervical cancer linked to earlier sexual debut. Low screening uptake had some effect on cancer risk, but number of sexual partners and smoking did not.

"Although women can be infected by HPV at any age, infections at a very young age may be especially dangerous as they have more time to cause damage that eventually leads to cancer," said Dr. Lesley Walker, director of cancer information at Cancer Research UK. "Importantly, the results back up the need for the HPV vaccination to be given in schools at an age before they start having sex, especially among girls in deprived areas."

The full report, "Differences in the Risk of Cervical Cancer and Human Papillomavirus Infection by Education Level," was published in the British Journal of Cancer (2009;101:865-870).