Nearly half of all cases of breast cancer might not be cancer at all. Instead, they may be harmless abnormalities that will not progress to cancer, claims an astonishing new report published in the latest issue of What Doctors Don't Tell You newsletter.

This could mean that 16,000 cases in the UK and 40,000 cases in the US could be aggressively, and unnecessarily, treated for cancer.

The misdiagnosis is caused by oversensitive mammography, and by a misunderstanding of the functioning of the breast. The first stage of one type of cancer is believed to be when a milk duct or lobule is invaded by microscopic calcifications. Most of these are so tiny that they cannot be seen or felt, and are only detectable on a mammogram. The calcifications are believed to be the precursors of cancer, but they are not in themselves cancerous. Nevertheless, they are misleadingly called 'carcinomas in situ' (CIS), which means 'cancers in place'. Doctors refer to the calcifications that occur in lobules as LCIS and the ones in ducts as DCIS, which is much the more common diagnosis of the two.

Before mammography, DCIS was virtually unknown, but it now accounts for up to 50 per cent of breast cancer diagnoses.

(Source: What Doctors Don't Tell You, February 2004; Special Report).

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