Study renews debate on Pap smear interval

EXPERTS are divided on the ramifications of a new Australian study which supports maintaining the current two-year interval between Pap smears.

The authors, from The Cancer Institute NSW, said their analysis provided evidence in support of retaining the two-year interval for women not vaccinated against HPV.

They studied Pap register data from more than 1.2 million women aged 20-69 years who had at least two Pap tests with the first one being negative.

The results suggested that if the screening interval was increased to three years, there would be an extra 1.9 cases of high-grade abnormalities per 1000 women, they said.

However, Dr Karen Canfell (DPhil), research fellow with the NSW Cancer Council’s Cancer Epidemiology Research Unit and a supporter of longer intervals, said the effect of screening intervals on invasive cancer was more important than that on rates of precancerous abnormalities.

The International Agency for Research on Cancer, which recommended five-yearly screening for women older than 50, and three yearly for younger women, had based its decision on the risks associated with developing invasive cancer, she said.

Gynaecological oncologist Dr Gerry Wain said progression rates had to be considered, in particular “whether a high-grade abnormality picked up at two years has any different outcome to one picked up at three years”.

He said ascertaining the optimum interval involved consideration of screening cost versus benefit.

The researchers found young women screened at three-year intervals had more high-grade abnormalities than those who screened two-yearly, but by the age of 50 years there was no significant difference between the interval groups.

Forty-three women (aged 23-66 years) had cervical cancer diagnosed within six months of the second Pap test.

The odds of being diagnosed with cancer increased by a factor of 1.66 with each year of increase in screening interval, the authors said. 

J Med Screen 2008;15:36-43.