Many women are expected to use the National Cancer Institute's change of heart as an excuse to avoid an examination they were never really comfortable with in the first place.
Having a mammogram is inconvenient, possibly expensive (even with mandated insurance coverage, there is usually a co-payment), uncomfortable and frightening.
"They might find something" is probably the leading reason why two-thirds of women have so far avoided this examination. Another common excuse is a fear that the X-ray examination itself might be harmful.
Mammography is now the only widely available, relatively inexpensive tool for finding breast cancers before they are big enough to be felt. But it is not a perfect tool.
Even when there is a lump a doctor can feel, mammography misses about 40 percent of cancers in younger women, three times as many as are missed in women over 50.
This should be a warning to all women with a suspicious breast lump: if the mammogram shows nothing, this does not mean the lump is benign and can safely be ignored or watched for many months without any other intervention.
All lumps should be investigated to determine whether they may be harmless fluid-filled cysts or tumors harboring cancer cells.
Mammography is also fallible in the other direction. It can pick up many lesions that may appear suspicious on the X-ray but are actually entirely benign. Since it is often not possible to tell merely from the X-ray which lesions can be safely ignored, most such findings prompt some sort of medical intervention, usually a biopsy in which the suspicious area is removed surgically and examined microscopically.
One concern about screening mammography for all women 40 and over every year or two is the large number of biopsies that it is likely to generate.
But Dr. Peter I. Pressman, a New York breast cancer surgeon, says that not every mammographic abnormality should touch off a surgical investigation. Rather, depending on the nature of the X-ray lesion, the area might be examined by a sonogram, a needle aspiration biopsy (an office procedure that does not involve surgery), another mammogram in three to six months, or nothing at all.
"Every finding on mammography doesn't need to be treated like Mount Everest," he says. "Newer techniques of dealing with mammographic abnormalities can keep women out of the operating room safely."
Another concern is that a negative mammogram can prompt some women to ignore symptoms of a possible cancer that appear between mammograms. Even if a lump is discovered within weeks of a negative mammogram, it should be treated as suspicious and looked at by a doctor, possibly with another mammogram.
Modern mammography using equipment that has been accredited by the American College of Radiology does not involve enough radiation to cause concern, even if mammograms are done each year for three or more decades. Eighty to 90 percent of mammography machines now in use have been checked to assure that they deliver the appropriate dose.
Dr. Daniel B. Kopans, a radiologist at Massachusetts General Hospital in Boston, urges women to choose a center that does 20 to 30 mammograms a day, to determine whether the technician does only mammograms and to ask to see the accreditation certificate.
Dr. Kopans also recommends that two radiologists read each woman's X-rays, since even the most competent doctor occasionally fails to see something significant that another doctor picks up. Double reading of mammograms is likely to be especially valuable for younger women because the X-ray differences between normal breast tissue and a malignancy are often harder to see in denser breast tissue, he says.