Breast cancers have become quite a scourge in recent times. What triggers them and whether women should get themselves screened have been subjects of much scientific debate. More revelations, it would appear, have only added to confusions and anxieties.
Two years ago, a couple of Danish studies wondered aloud if screening breasts for cancer was effective at all. That left many women in a frustrating quandary. Now, a WHO-sponsored study concludes that mammography does save lives, at least for women aged between 50 and 69. The study cautions that the benefits for younger women are uncertain.
The International Agency for Research on Cancer (IARC) in Lyon—an international group of independent cancer experts—reviewed all the available scientific evidence on screening and concluded that "a 50-year-old woman undergoing screening regularly every two years can expect about a 35 per cent reduction in her risk of death from breast cancer."
The IARC/WHO findings support other new data. For example, a Swedish study in The Lancet found a 21 per cent reduction in breast cancer deaths in women who had been offered screening. However, the IARC's report concedes that screening is a double-edged sword. Regular X-ray exposure during mammography can not only cause a small number of cancers, but it could also reveal tumours that may not have produced symptoms during the woman's lifetime. This can mean unnecessary and distressing treatment. Hence, the doubts over benefits to younger women.
Debates over breast cancer's probable causes are no less vexatious. According to another breast-cancer study involving 91,000 women, women who defer motherhood until their thirties are more prone to developing breast cancer.
Francoise Chavel-Chapelon and colleagues at INSERM, the French National Institute for Health and Medical Research, tracked the women, aged between 40 and 65, over a decade. Compared with women who gave birth before the age of 22, those who had their first child in their thirties were 63 per cent more likely to develop breast cancer before the menopause, and 35 per cent more likely to develop the disease afterwards. Women who remained childless had the highest risk of all. Changes to breast cells in the third trimester of pregnancy are thought to protect the breasts from cancer.
The link between reproductive factors, fluctuation in hormones and women's breast cancer risk is extremely complex, and previous small-scale studies have often produced confusing and conflicting results. Researchers say only by looking at very large numbers of women, as this study has, can they start to build up a picture of how and why breast cancer develops.