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In the latest challenge, two Danish researchers who reviewed the major clinical trials of screening mammography declared that five of the seven trials were flawed and that none demonstrated that it saved lives. Other experts have challenged the validity of their analysis and contend that the preponderance of evidence is that mammography is lifesaving.

Many women whose confidence in this widely used early detection technique has been shaken are now wondering if they should abandon their yearly mammograms and wait for a hand in the shower or bed or examining room to find a palpable tumor. Or should they continue to take advantage of a tool that has been proved to be able to find breast cancers before they grow to a size that can be felt?

The American Cancer Society said it saw no reason to change its recommendation for annual screening; a panel convened by the National Cancer Institute declared that the evidence does not support such a recommendation.

So once again, women must make a major decision amid rancorous medical disagreement. I have opted to continue having yearly mammograms.

Lives Are Being Saved

While the scientific and political issues that cloud the value of screening mammography are complex, some facts cannot be ignored. First is the fact that since mammography has become widely used, tumor size at the time of detection has declined and so has the death rate from breast cancer.

In the early 1980's, when only 13 percent of women in the United States were getting mammograms, the average tumor size at detection was about three centimeters. By the late 1990's, when 60 percent of women were having regular mammograms, the average tumor size had shrunk to two centimeters, according to data from the Cancer Society and the National Center for Health Statistics.

This decline in tumor size may sound trivial, but it is not. The larger the tumor, the longer or faster it has been growing. Studies have shown that larger tumors are more likely to have spread beyond the site in which they arose. This, in turn, may mean that more aggressive treatment is necessary to improve a woman's chances of surviving the disease. Even with more treatment, on average, the survival chances of a woman with a large tumor are not as good as those of a woman with a smaller tumor.

There are exceptions, of course. There are some tumors, though small when discovered, that are highly aggressive and may spread despite early discovery. And some small tumors are rather indolent and never become threats.

The trouble is, it is not now possible to distinguish between these two states with any degree of certainty, although it may be in the future. Many researchers are studying the molecular characteristics of different cancers to try to categorize them as more or less life-threatening and thus warranting different degrees of treatment, including no treatment at all.

According to my reading of the evidence, finding breast cancers earlier through mammography, along with early treatment, has resulted in a steady decline in death rates of nearly 2 percent a year since 1990. While improvements in treatment have undoubtedly contributed to the decline in deaths, there is evidence that early detection has made a major contribution.

At the same time, earlier detection has made it possible to treat many more cancers with lumpectomy instead of mastectomy without compromising a woman's survival chances.

For example, one 29-year follow-up of breast cancer deaths in two Swedish counties published last year revealed a 63 percent decline in the death rate among women who received regular mammograms and no decline in the death rate among the women who were not screened, even though the same improvements in treatment were available to all.

"This study corroborates the results of the clinical trials of screening mammography," said Dr. Daniel B. Kopans, director of breast imaging at the Massachusetts General Hospital in Boston and an advocate of screening mammography.

One issue raised by the Danes is that treatment for breast cancer, which may not always be necessary, may increase deaths from other causes, particularly heart disease. The increase in cardiac deaths cited in that study, Dr. Kopans contends, resulted from rather primitive radiation treatments administered in the 1960's.

Good but Not Perfect

No one is claiming that mammography is a perfect screening tool. There are sometimes false-negative results: in women under 50, mammography is likely to miss 20 to 25 percent of existing cancers, and in women over 50, it misses 8 to 10 percent.

For this reason, when a woman or her physician feels a suspicious breast lump that does not show up on a mammogram, it should be examined by some other means — sonography or biopsy. Watching such a lump for months could compromise a woman's survival chances if it turns out to be cancer.

Another problem with mammography is that sometimes it suggests a problem where none exists — the so-called false positive, creating temporary anxiety and necessitating a repeat examination and possibly a biopsy.

It is also likely that some small percentage of breast cancers that cannot be felt but show up on mammograms will never grow to a point of threatening the women's lives. These women would then undergo treatment they did not need. In my opinion, this may be a necessary price to pay for the chance to save the lives of the much larger number whose cancers will be life-threatening if not for early detection and treatment.

There is another indirect potential benefit to screening mammography: it helps to create a mind-set focused on maintaining health, prompting women to seek information and treatment and to get good medical care.

Having reviewed the arguments pro and con screening, I plan to continue to get annual mammograms.

Regular readers of this column know that I have had a breast cancer that was detected early but not by a mammogram. My routine mammogram showed nothing, but the manual breast exam done by the radiologist suggested something suspicious, which was then examined by ultrasonography and a biopsy, revealing a malignancy.

The tumor was only about one centimeter, small enough that I could be treated with a lumpectomy and radiation therapy. So you could argue that going for my annual mammogram was much to my benefit. I am hardly alone. Many thousands of others have had similar experiences, benefiting directly or indirectly from early detection through mammography.

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