Health watch: Mammography: Staying informed
Although heart disease and lung cancer cause more deaths, American women generally are more concerned about the chance of getting breast cancer – and with good reason.
Of about 275,000 women expected to be diagnosed with breast cancer this year, more than 40,000 eventually will die and most of the rest will experience significant physical and emotional trauma.
About 70 percent of American women respond by getting screening mammograms at least every two years.
While far from perfect, mammography still is the best method readily available to detect breast cancer at an early stage and is recommended by the American Cancer Society, the U.S. Preventative Services Task Force, the American Medical Association and most other medical groups. Doctors believe it reduces the risk of death by about 25 percent, although that issue is still being debated.
A mammogram consists of two sets of X-rays of each breast – one view from the top and another from the side. Although the procedure can be uncomfortable as the breast is pressed firmly between two plastic plates, it takes only about 20 minutes, is inexpensive and exposes a woman to a minimal dose of radiation – about as much as she would get in a long-distance flight from New York to Los Angeles.
Mammography is very sensitive and can detect cancer one to three years before it can be felt as a lump or produce any symptoms. In most cases, these early tumors can be treated successfully, although some aggressive cancers are difficult to stop even when detected at this stage.
The downside is a false positive rate. About five to 10 percent of women have abnormal mammograms requiring further procedures while fewer than 1 percent end up with a diagnosis of cancer. These women experience substantial anxiety as well as painful and invasive diagnostic procedures. And a biopsy may produce scar tissue that makes it difficult to detect suspicious growths in the future.
In addition, mammography frequently detects small cancers known as ductal cancer in situ, DCIS, some of which may remain harmless and pose a treatment dilemma. Since it’s difficult to distinguish between harmless DCIS tumors and those likely to become invasive, many women undergo treatment that may or may not be necessary. Mammography also produces false negatives, failing to detect some cancers.
Older women benefit more
The usefulness of mammography is somewhat age-related. Younger women have denser breasts with more glands and ligaments making it difficult to spot abnormalities. After age 50, a woman’s breasts have a higher percentage of fatty tissues, which shows up as gray on the mammogram compared to the white areas that may represent abnormal masses.
For women older than 50, there’s little controversy. Most groups recommend an annual screening.
For women in their 20s and 30s, mammography has little usefulness, and for women between 40 and 49, there’s still debate about whether and how often it should be done. Breast cancer is much less common in younger women, but it also tends to grow faster and more aggressively.
The American Cancer Society now recommends mammography every two years for women in this age group.
Women considering mammography should be familiar with the concept of sojourn time – the length of time during which a cancer can be detected on a mammogram before the onset of a lump or other symptoms.
The sojourn time is 1.7 years for women aged 40 to 49, but 3.3 years between ages 50 and 59 and 3.8 years between 60 and 69. As a result, many doctors advise women in their 40s to get mammograms at least every year and a half.
In the United Kingdom, all women between the ages of 50 and 69 get a free mammogram every three years, and breast cancer mortality is about the same as that in the United States, where more frequent screening is recommended.
Some studies during the past decade have questioned the benefit of mammography at any age. Two large Canadian studies, both started in 1980, found that screening resulted in only a 3 percent reduction in deaths for women older than age 50 and an increase in deaths for younger women.
More recently, Danish researchers reviewed seven large randomized controlled studies of mammography and decided that five of these trials – those showing the greatest reduction of mortality – were too flawed to use. Women in the study group and those in the control groups were not properly matched in terms of age.
Deaths from uncertain or multiple causes were sometimes attributed to breast cancer in the control groups and death related to treatment of breast cancer were often overlooked. In the two studies they retained, the Canadian study and a Swedish study, the Danish researchers found insufficient evidence that mammography reduced cancer deaths or deaths from other causes.
A panel of experts convened by the U.S. Preventative Services Task Force disagreed with the Danish analysis, deciding that the flaws did not invalidate the conclusions of the five studies. And a team of New York scientists, writing in The Lancet, contended that, using an inadequate period of screening and followup data from the Swedish study confirmed a significant benefit.
The death rate was 55 percent lower for women age 55 and older who were screened and followed for 8 to 11 years than those who were not screened.
A later study published in The Lancet found that in the long-term, women getting regular mammograms had a 21 percent reduced risk of dying from breast cancer. The decreased risk was even higher for women in their 60s – 33 percent.
Most American women, on the advice of their doctors, continue to get regular mammograms. In many cases, a woman operates on the belief that a tumor detected early may allow her to choose a less invasive option, such as lumpectomy. A lumpectomy removes the cancerous growth plus a margin of healthy tissue surrounding it, but not the entire breast.
As less invasive, less disfiguring treatments and diagnostic tests become available, mammography is likely to look ever more attractive as a way of detecting early cancer.
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