Mammography & breast cancer: sometimes what you see is not what you get.

Since the very first study of mammography in the 1960s, everyone has assumed that the breast cancers found via screening mammography were exactly the same as any other breast cancer. After all, the final diagnosis of breast cancer isn't made until after the suspicious tissue is examined in several different ways to determine not just that the cells are cancerous, but also in what ways and how aggressively the cancer is expressing itself. Women are told whether or not their breast cancers are responsive to hormones and whether the cells have extra copies of the Her2neu gene, just to name two of the most common tests performed on breast cancer tissue samples. A new study has raised the possibility that, even though a mammography-detected cancer may look exactly like other breast cancers, it may be different in one important aspect: it may have the potential to go away on its own. (1)

The study took advantage of the Norwegian commitment to health care for all and excellent record-keeping. Norway introduced mammography screening in 1996 and, since then, almost every woman aged 50-64 has taken part in the screening program. The study looked at the difference in the numbers of cancers found over six years in women who were screened every two years starting at age 50 versus the number found in women who were about five years older when screening started and were only screened once (for the study). The researchers assumed that the women only screened once would have slightly fewer cancers detected, because a single screening mammogram always misses a few cancers. They were surprised when the cancer registry data showed that many fewer cancers were detected in the women screened once in their mid-50s compared to those who were screened three times between age 50 and 56. Screening regularly resulted in the diagnosis of 191 ...