Mammography Q&As

I have just had a mammogram and the specialist said it showed microcalcification. What does this mean?

A number of conditions can lead to traces of calcium forming in the tissues of the breast. Microcalcification is the name given to tiny specks of calcium, less than 1mm in size, which show up as bright white spots against the grey/black background of the mammogram picture.

About 4 out of 10 breast cancers contain clusters of microcalcification. Microcalcification is even more common in the precancerous condition of ductal carcinoma in of the breast (DCIS) where it is seen in about three quarters of all cases.

In mammograms used for screening for breast cancer microcalcification may be the first sign that a cancer is present, with clusters of calcium specks showing up even though there is no lump to feel and no tumour showing on the mammogram film.

Microcalcification does also occur with a number of completely benign, non-cancerous, breast conditions including fibroadenomas and papillomas. Very often the specialists can tell from the shape and pattern of the calcium specks whether or not there is likely to be a cancer present.

If there is any uncertainty as to whether the microcalcification is due to cancer, or precancerous DCIS, then your doctors will almost certainly arrange a biopsy to get a definite answer. This involves taking a tiny piece of breast tissue and is usually done with a needle and a local anaesthetic in an outpatient clinic.

I do not understand why a breast cancer can appear in the two years between mammograms for screening, when doctors say it takes many years for a breast cancer to develop.

We believe that cancers usually start with abnormal changes in just a single cell, or a very small number of cells, in a particular part of the body. Over a period of time these cells multiply, and eventually form a tumour.

Usually the earliest a breast cancer, or any other type of cancer, can be detected is when it is about 0.5cm (about 1/4 inch) across - and most are only discovered when they are several centimetres in diameter. By the time a cancer has reached a diameter of 0.5cm it will contain about a hundred million cells, and will have been growing for a long time, probably quite a few years.

Mammograms can first detect breast cancers when they are between about 0.5–1cm across, smaller tumours are very unlikely to show up on the x-rays. This means that although from a medical point of view we say that mammograms can detect breast cancer at any early stage, when it is still highly curable, these 'early' cancers will actually have been growing for a long time, but will have been completely undetectable by any of the tests that we have at the present time.

If someone has a normal mammogram, and then two years later, when the test is repeated, it shows up a small cancer in their breast, this doesn't mean that the tumour first started during the interval between the x-rays, but simply that it has grown to a size when it can be seen on the mammogram during that two year period - the cancer itself will almost certainly have first started some years before, but was simply too small to show up on the early x-ray films.

Incidentally, when a new breast cancer appears in the two years between screening tests, doctors often call these 'interval' cancers, since they have become detectable in the interval between mammograms.

How common are false negative mammograms when you are being checked for breast cancer?

Mammograms are a very reliable way of detecting breast cancers but they are not foolproof. Around about one in ten breast cancers will either not show up at all on a mammogram or will look like a complete benign, non-cancerous, abnormality. These are called false negative results, since they suggest there is nothing to worry about, when in fact there really is a cancer in the breast.

For women who are attending a Breast Clinic after having found a breast lump the small chance that the mammogram is a false negative is less of a problem because the mammogram forms only one part of what is known as a 'triple assessment'. The triple assessment involves an examination of the breast by a specialist, a mammogram and a fine needle aspiration. (cells from the lump being removed by a special needle, with a local anaesthetic). The combination of these three techniques means that the correct diagnosis will almost always be made.

False negative mammograms are more of a problem in breast cancer screening, where women who have apparently normal breast have the test in order to detect small cancers with have not yet become apparent. If the mammogram looks normal then no further action is taken, so a false negative examination does mean that cancer can be missed. The chance of this happening has been reduced in recent years with the introduction of 'two-view' mammography into the UK screening programme in 1995. Before this screening often involved a single x-ray picture of each breast but it was then shown that taking two pictures from different positions increased the cancer detection rate by up to 25%. So, although it is more expensive and time consuming, the two view method has now become standard.

Although mammographic screening will still inevitably miss some early cancers it remains the best screening method there is and still detects very many unsuspected tumours every year when they are still at an early, curable, stage.