In a study published in The Lancet, the experts said a visual screening test to look for the early signs of cervical cancer reduced the numbers of cases by a quarter.

“This is a landmark study,” said Dr Harshad Sanghvi, medical director at JHPIEGO, an affiliate of Johns Hopkins University, which has worked on preventing cervical cancer in poor countries. Sanghvi was unconnected to the Lancet study.

Cervical cancer is largely preventable. It causes about 2.5 lakh deaths every year and is the second-most common cancer in women. Nearly 80 per cent of those women are in the developing world.

The test can be done by a nurse or trained health care worker, who washes a woman’s cervix with vinegar and gauze using a speculum to hold it open. After one minute, any pre-cancerous lesions turn very white and can be seen with the naked eye under a halogen lamp.

Officials used the technique among a group of 49,311 women in Dindigul district in Tamil Nadu from 2000 to 2003.

When pre-cancerous lesions were found, health care workers gave immediate treatment to destroy the abnormal cervical tissue.

Another 30,958 women received standard care. They were told to watch for signs and symptoms of cervical cancer and encouraged to visit healthcare facilities where screening was available. These women were tracked from 2000 to 2006.

There were 167 cases and 83 cervical cancer deaths in the women who received the screening, compared with 158 cases and 92 deaths in those who didn’t. That represents 25 per cent less cervical cancer and a 35 per cent lower death rate among those screened.

All of the women in the study were healthy and between 30 and 59 years old. The research was funded by the Bill & Melinda Gates Foundation.

Previous research has shown that the visual screening technique is almost as effective in catching cancer as pap smears, a more expensive technique used in the West.

“This is the final proof that with an extremely simple test, we can have a dramatic impact on cervical cancer rates,” Sanghvi said.

Still, the test isn’t perfect. It can produce many false positives, so healthcare workers giving the test must be properly trained. Also, the test cannot be used in post-menopausal women or in women who have had more than two or three children, since pre-cancerous lesions in those women develop in parts of the cervix not normally visible.