KEY POINTS:
A marked reduction in New Zealand's breast cancer rate is being linked to the plummeting use of hormone replacement therapy by women.
The breast cancer rate fell 6 per cent in 2003 - the latest year for which figures are available - slightly less than the 7 per cent drop recorded in the United States.
That was the year after a large American study of combined oestrogen-progestogen HRT was stopped early because it found the treatment increased the risk of breast cancer and several other conditions.
Tighter controls were imposed on HRT, and use of its drugs - prescribed to alleviate hot flushes and other menopausal symptoms - immediately dropped.
In New Zealand, HRT prescriptions have levelled off at about a third of the number in 2001. The number of prescriptions written increased rapidly during the 1990s.
Breast cancer experts internationally are tentatively drawing a connection between declining rates of new breast cancer, especially among older women, and lower HRT use.
"There is on the face of it a decline in the numbers, which may be related since 2002 to the decline in hormone replacement therapy," said the clinical leader of the national screening unit's Breast Screen Aotearoa, Dr Madeleine Wall, yesterday.
"We need to crunch the numbers and we have to wait another year to do that, but it would be fabulous if it were proven to be true."
The screening programme detected 581 breast cancers in women aged 50 to 64 last year, compared with 623 in 2002, the peak year since the scheme started in 1998.
Dr Wall said the reduction could also be related to the mammography screening programme's having been running long enough to be past the initial increase in cancer detection that went with its introduction.
St Marks Breast Centre physician Dr Jenny O'Sullivan said: "I suspect the reduction may be in part from a reduction in hormone replacement therapy, but there may be other reasons affecting it as well."
A University of Texas study found the 7 per cent drop in the US breast cancer rate "may largely be due" to many older women stopping HRT.
The steepest breast cancer decline, of 12 per cent, was among women aged 50 to 69 with oestrogen-receptor-positive breast cancer, which depends on hormones for tumour growth.
The study's lead author, Professor Donald Berry, said that although breast cancer took a long time to develop, "here we are primarily talking about existing cancers that are fuelled by hormones and that slow or stop their growing when a source of fuel is cut".
"These existing cancers are then more likely to make it under mammography's radar."
The study which sparked the decline in HRT use recorded 38 breast cancer "events" per 10,000 women using the drugs a year, compared with 30 among those not using them - a 26.7 per cent increase in relative risk.
New Zealand health authorities then warned that HRT should be used only for troublesome hot flushes and night sweats and in the lowest dose for the shortest possible time.
CANCER AND HORMONES
* New breast cancer cases per 100,000 population: 2001, 86.6; 2002, 86; 2003, 80.9. In 2003, that was 2297 women.
* 19 per cent of women aged 45-64 were using hormone replacement therapy in 1997; the figure was down to 11 per cent by late 2002.
Sources: Health Information Service, Otago University and Breast Screen Aotearoa.
