In the wake of the National Cancer Institute's decision to stop recommending regular mammograms for women in their 40s, many radiologists and other doctors who treat patients continue to be convinced by their clinical experience and intuitive reasoning the benefit of routine screening for these women would be obvious if the proper studies were done.
Meanwhile, women and their doctors are left in a quandary about the best use of this weapon for early detection of breast cancer, the disease women fear most.
The statisticians upon whose assessment public health policy is largely based want to see significant evidence that mammography offers life- saving benefits to women younger than 50. Critics say studies of screening mammography done so far have included too few women in their 40s and did not follow them long enough.
What is a woman to do if she is under 50, healthy and has no suspicious lumps or strong family history of breast cancer? Should she wait until menopause to begin annual mammography, or should she start at 40?
Even the cancer institute's director, Dr. Samuel Broder, seems torn between how he would advise individual patients and what he would say to the general public. As he told the National Cancer Advisory Board Subcommittee on Women's Health and Cancer: "What I would do as an individual is recommend annual mammograms. But I can't recommend it to the public because I don't have the facts."
The institute's decision to recommend routine mammography for women over 50 but not for younger ones was prompted by a lack of statistically significant evidence that screening mammography can reduce deaths among younger women, as it has been repeatedly proved to do among women in their 50s. Statistical significance is a way of determining that the finding was unlikely to have been a result of chance.
Yet many radiologists and some of the researchers who conducted the studies on which the institute's decision was based, insist the existing evidence, though not statistically certain, indicates women of all ages can benefit from periodic mammograms. These low-dose X-ray examinations can reveal the presence of breast cancers long before they grow large enough to be felt.
In some women, including those under 50, mammography finds cancers at a microscopic stage, when the cure rate is as high as 90 to 95 percent. A major source of concern, however, is that these include an unknown percentage of malignancies, called in situ cancers, that would never have become invasive and life-threatening, meaning that surgery to remove them is unnecessary.
The problem arises because, as is pointed out by Dr. Robert Hutter, a former president of the American Cancer Society who is a pathologist at St. Barnabas Hospital in Livingston, N.J., "the pathologist really can't tell which cancers diagnosed microscopically will progress and which will not."
Another reason it has been hard to prove a benefit, some radiologists suggest, is that only 30 to 40 percent of younger women could expect to be helped by screening mammography because of the growth rate and characteristics of their tumors.
Despite such concerns, as medical researchers have come to better understand the biology of breast cancer in younger women, many have concluded that for mammography to achieve its maximum lifesaving benefit, women under 50 should have the X-ray examination more often than those over 50.
Analyses by researchers at the University of Nijmegen in the Netherlands and at the University of Cincinnati have shown that in women in their 40s, breast cancer typically progresses twice as fast as in older women from a microscopic lesion detectable only by mammography to a tumor large enough to be felt by an examining hand.
This shorter time to prepare may explain in part why studies of mammography's lifesaving potential have so far shown a statistically significant benefit only for women in their 50s. In older women, mammography done every year or two has more of an opportunity to pick up cancers while they are still confined to the breast and curable.
Based on their analyses of tumor growth rates, Dutch researchers and radiologists in this country have concluded that mammography, along with a physical examination by a doctor, should be done once a year.