Nationwide audit of screening programme reveals failure to be screened at recommended intervals is major risk factor for cervical cancer

Failure to be screened for cervical cancer at the recommended time intervals is the major risk factor associated with developing the condition, according to the first nationwide audit of a cervical cancer screening program, which also revealed that it was equally effective for women of all ages.

Cervical cancer is the second most commonly diagnosed cancer in women across the world. The incidence has been reduced in many countries by the introduction of Pap smear screening programmes (named after George Papanicolaou, the doctor that developed the technique). These reduce the incidence of cervical cancer by enabling detection and removal of precancerous lesions in the cervix, as well as reducing deaths by detecting and treating cervical cancers early. The effectiveness of screening programs has varied substantially between different countries but the reasons for this have been unclear.

Researchers audited the cervical cancer screening program in Sweden to try to find how different factors influenced its effectiveness. They compared all 1230 women diagnosed with invasive cervical cancer (cancer that has spread deeper than the surface of the cervix) in Sweden during 1999-2001 to age-matched controls who did not have cervical cancer.

In particular, they looked at the women’s participation in the cervical screening program over a six-year period using the National Cervical Cancer Screening Register. The Swedish program recommends Pap smear screening every three years for women aged 23-50 years, and every five years for those aged 51-60 years.

Results showed that women who had not had a Pap smear during the recommended screening interval were more than two and a half times as likely to develop cervical cancer than those who had been screened (odds ratio 2.52, 95% confidence interval 2.19 to 2.91). This risk was increased for all age groups. Women who had not had a Pap smear within the recommended screening interval had a particularly high risk (increased nearly five-fold) of advanced cancers (OR=4.82, 95% CI 3.61 to 6.44).

“As expected, we found that not having had a Pap smear taken within the recommended screening interval was the most important risk factor for cervical cancer in the presence of a screening program. Approximatly 64% of all cervical cancers and 83% of the advanced cases were diagnosed in women who were not tested,” reported the researchers.

Screening was also associated with decreased risks of cervical cancer among women who were younger than 30 or who were older than 65 years. The research group concluded: “These results indicated that compliance with screening recommendations and high population coverage of screening are vital for success and that attention should be paid to underscreened older women.”

Abnormal smears, particularly if not followed up by a biopsy, were also an important risk factor for cervical cancer (OR=7.55, 95% CI 5.88 to 9.69). The results showed that just over one in ten (11.5%) of women with cervical cancer had had an abnormal smear. “This suggests improved follow-up programs are warranted,” the researchers added.

In an accompanying editorial, Jack Cuzick, from the Cancer Research UK Centre for Epidemiology, Mathematics, and Statistics, Wolfson Institute of Preventive Medicine, London, UK, commented, “Screening is a large-scale, repetitive "industrial process" and, as with all other such processes, one can learn most about its performance by examining the failures—a woman who is eligible for screening and who develops a potentially fatal cervical cancer—and then retuning the process accordingly.” The fact that 32% of all cancers and an even greater percentage of late-stage tumours appeared in women older than 65 years