Women are still at risk of developing cervical cancer 25 years after being treated for precancerous lesions, according to a new study.
Experts are now calling for cytological smears to be offered at regular intervals for at least 25 years after a woman has had severe dysplasia/CIS (carcinoma in situ).
CIS is not cancer, but is similar to it as some cells look cancerous but are in the soft layer that lines body cavities.
Researchers in Sweden studied 132,493 women who had been diagnosed with severe dysplasia/CIS, and found that 881 of them developed cervical cancer and 111 women had vaginal cancer more than one year after the diagnosis.
It means women who have had CIS are more than twice as likely to develop cancer as the general female population.
The authors of the study, which is published in the British Medical Journal (BMJ), said: "Although most women with high-grade dysplasia have been protected from invasive cancer it must be considered a failure of the medical service when women participate in screening, their precancerous lesions are found and they subject themselves to treatment of those lesions, presumably participate in follow-up programmes and still develop invasive cancer."