VOA慢速英语 2007 0516a（在线收听）

This is the VOA Special English Health Report.

Research is often a slow, maddening search for answers where each new finding only seems to raise more questions. 

This is the case with a story we told you about last month. It offers a good example of how difficult it can be to define a relationship between two events, or even prove a connection.

 
 
In this case, one event was a sudden drop in the use of hormone replacement therapy. The other, which followed, was a sharp drop in the breast cancer rate in the United States. 

Many older women stopped taking hormones after a government warning in two thousand two about possible risks.

Last December a team of scientists reported that breast cancer rates fell in two thousand three. Then, last month, they reported that the breast cancer rate was still down in two thousand four. They suggested that the major cause was most likely the drop in hormone use.

For evidence the researchers presented two main findings. One was that the reduction in the breast cancer rate was greatest among cancers fed by estrogen. Estrogen is commonly used in hormone replacement therapy. The other finding was that the reduction happened mainly among older women -- the main users of the therapy.

The scientists suggested that going off hormone therapy reduced the risk of cancer growth. They said other explanations for the drop in the breast cancer rate were possible, but less likely to have played a big part.

Now, a new study looks at one of those other possible influences: a decrease in mammogram testing for breast cancers. The study by the American Cancer Society just appeared in the journal Breast Cancer.

First, the study shows that breast cancer rates began to fall in nineteen ninety-nine. That was three years before the government warning about hormone therapy.

Secondly, the study shows that after the warning, fewer women had mammograms, which are usually done with X-rays. A mammogram is required before starting hormone therapy.

Whatever the reason for the decrease, fewer tests would mean fewer chances to find cancers. Still, many experts believe that the drop in estrogen-fed cancers in older women had something to do with the drop in hormone use.

A final note: government researchers reported Monday that mammogram testing fell four percent between two thousand and two thousand five. The lead researcher called it "very troubling."

And that's the VOA Special English Health Report, written by Caty Weaver. I'm Barbara Klein.