Introduction

A screening mammogram is one obtained in a healthy woman who has no lump or other significant symptom related to her breasts. The purpose is to find breast cancer at an early stage, before it has produced a lump.

While the need for regular manual examination (palpation) of the breasts is universally accepted, women are often given less enthusiastic or even negative advice regarding screening mammography. Yet mammography, despite its imperfections, is one of few methods for early cancer detection that has been proven in extensive trials to reduce the death rate from the disease in question. This booklet aims to present to the concerned woman an objective look at this screening technique, its strengths and weaknesses, to help her make her own, rational, decision.

Why do I need a routine mammogram?

Most women are acutely aware of the devastating effect that the diagnosis of breast cancer has on the life of a woman. Many do not realise that early diagnosis significantly reduces the risk of dying of this disease and may allow treatment without mastectomy.

In the breast, as in other parts of the body, there is normally a steady, controlled replenishment of the cells that make up that tissue. Cancer is the result of this normal process becoming uncontrolled with cells multiplying rampantly until they form a lump. This lump, initially too small to see or feel, grows in size until it becomes visible on a mammogram and, usually a considerable time later, big enough to feel. At any point in this evolution cancerous cells may spread via the blood or lymphatic vessels to other parts of the body, an event which dramatically worsens the prognosis. Cancer found at a stage when it is visible on a mammogram but cannot yet be felt is much less likely to have spread in this way than cancer which is advanced enough to feel. The purpose of routine, screening mammography is to find breast cancer at a very early stage, enabling surgery and possibly radiation therapy to curtail the natural evolution of the disease before it spreads to other parts of the body.

At what age should a woman have her first routine mammogram?

Routine mammography is not recommended for women who are less than forty unless there is a family history of breast cancer at a young age. The reasons for this include difficulty in interpreting the image of the densely glandular young breast, increased sensitivity of the young breast to radiation and the lower incidence of breast cancer in younger age groups. None of these factors undergoes a rapid and dramatic change at any particular age and defining an 'official' starting point for routine mammography will always be a little arbitrary. Reduced mortality rates attributable to screening mammography have been demonstrated from 40 years of age and the American College of Radiology and the American Cancer Society, amongst others, recommend this as the age at which routine mammography should commence.

How frequently should mammography be performed?

Frequent mammography promotes the early detection of breast cancer but this must be balanced against the need to limit radiation and costs. It has been shown that increasing the inter-mammogram interval to longer than a year considerably compromises its ability to reduce the death rate from breast cancer. This is especially true in the 40 to 49 year age category in whom breast cancer is less common but often more aggressive than in older women.

Imagine that an office block has a fire surveillance system that samples the air in each room periodically to detect smoke. If statistics showed that, on average, it takes 15 minutes for a fire to become uncontrollable, would it make sense to sample each room every half-hour? I think a sampling interval of well under 15 minutes would be far better. Similar reasoning strongly favours annual mammography.

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