Last Updated: 2003-06-02 10:01:48 -0400 (Reuters Health)

LONDON (Reuters Health) - The number of British women diagnosed with breast cancer each year has reached its highest level ever, topping 40,000 for the first time, according to new figures released on Monday by a leading charity.

Cancer Research UK said the number of cases would keep increasing for some time, but screening and improved treatments meant more women are being successfully treated than ever before.

Currently, three out of four women diagnosed with the disease survive for five years or more, and annual death rates have dropped 21 percent over the past 10 years to around 13,000 in 2001.

"Tamoxifen has been in use for 20 years and the screening programme has been up and running for the last 15. These two advances alone account for significant improvements in survival," said Professor Jack Cuzick, head of Cancer Research UK's epidemiology, mathematics and statistics department at the Wolfson Institute for Preventive Medicine in London.

He said the reasons for the increasing number of cases were harder to understand, but were related to levels of the female hormone oestrogen.

"We know that obesity in post menopausal women is a risk factor and that it can raise the levels of oestrogen. We also know that levels of obesity have been rising steadily in the past decade and this may be contributing to the upward trend."

Genes also play a role, as do late menopause and the early onset of periods, which can also increase exposure to the hormone, he said.

The charity's clinical director Professor Robert Souhami said research was beginning to uncover the factors that affect risk.

"In the meantime, early detection remains very important in preventing deaths from breast cancer and it is essential that women are aware of this and attend for screening when they are invited."