A British investigation into breast-screening which found a
concerning rate of over-diagnosis indicates about 180 women
will be treated unnecessarily each year in New Zealand,
University of Otago cancer-screening authority Associate Prof
Brian Cox says.
Unnecessary treatment included mastectomy, radiotherapy, and
The Government should consider whether this was a good use of
resources, he said.
Prof Cox extrapolated from the findings of an independent
panel in the United Kingdom, which said about one in four
women diagnosed with breast cancer through screening would
never have had a problem had it not been identified by
Some disease does not develop into clinical cancer, but
screening does not distinguish between what is dangerous and
what will not cause a problem.
"This over-diagnosis of sub-clinical disease that would not
develop into clinical cancer in a person's natural lifetime
results in investigation and treatment, and the side effects
of treatment ... "
While the over-diagnosis problem with screening programmes
was well known, the rate, about 19%, was higher than previous
"Resources could be better spent on other aspects of breast
cancer care and prevention than screening women under 50," he
When calculating New Zealand's figure, he took account of the
fact its screening programme admitted women aged from 45-69,
whereas Britain's lower age level is 50.
New Zealand was out of step with other countries in its lower
"The evidence regarding the balance of harm versus benefits
was not strong enough to reduce the age of screening in the
programme [from 50] to 45 years of age, as was done in July
Over-diagnosis potentially increased with lower entry ages to
programmes, because more screening took place.
However, he noted uptake had been lower in the 45-49 age
group in New Zealand.
"The breast-screening programme here has had some difficulty
getting women 45-49 to participate." Prof Cox said about 60
of the 180 women treated after screening would be diagnosed
with invasive breast cancer. The rest would be told they had
ductal carcinoma in situ.
"Currently, it is not known how many deaths from breast
cancer are prevented by breast-screening in New Zealand,
although it has been shown that the reduction in the annual
number of deaths from breast cancer from screening women
under age 50 years can be expected to be very small."
New Zealand Breast Cancer Foundation medical adviser Dr
Belinda Scott said the key issue was promoting medical
advances to allow better identification of which women
The breast-screening programme saved lives, even if some
women did undergo unnecessary treatment, she said.