AAAS annual science meeting: There is no doubt that cancer screening saves lives, but it also has a serious downside. False positives and the trauma for many women of submitting to tests has a potential and as yet unquantified impact on health.
A number of speakers addressed the issue of cancer screening as the American Association for Advancement of Science annual meeting in Washington drew to a close. They highlighted the clear benefits of screening as a way to reduce cancer mortality but acknowledged that too much screening delivered diminishing returns.
Dr Sandra Lee of the Dana Faraber Cancer Institute described efforts to create mathematical models predicting the reduction of breast cancer mortality due to screening. The goal was to measure one screening regime against another.
"We are not advocating any particular interval for mammography screening," she said. "We have developed mathematical models. Our main goal is to assess mortality versus screening." She described some of the problems involved for policy-makers looking at the issue. The US Cancer Society advocates annual screening for all women aged over 40. The UK suggests screening at three-year intervals for women over 50.
Which will reduce mortality better, Dr Lee added.
She looked at different screening frequencies in women from 50 to 79 with an average breast cancer risk. Annual screening reduced mortality risk by 37 per cent. Screening once every two years reduced risk by 30 per cent and by 26 per cent for once in three-year screening.
Beginning mammograms at age 40, when breast cancer risk is low, reduces overall risk of death by 5.3 per cent. Yet the disease is more aggressive if it occurs in the 40 to 50 age bracket and so Dr Lee argued that starting early may have merit.
If women underwent mammograms every two years beginning at 40 and then annually starting at 50, there would still be a 33 per cent reduction in mortality.
The value of screening is much easier to assess in cervical cancers, said Dr Diane Solomon of the US National Cancer Institute. "Cervical cancer mortality has dropped by 70 per cent over the last 50 years largely because of the screening programme."
While there were "inherent limits" to the pap test, with the potential for false positives and false negatives, the test served women. False positives in particular "can become a burden as well", she said.
Between 5 and 10 per cent of women in the US never received a pap test and this group accounted for half of all cervical cancer deaths, Dr Solomon said. "Where we see an absence of screening we still see very high mortality rates."