How much does anastrozole actually help? The numbers explained

Anastrozole lowers the chance of hormone-receptor-positive breast cancer coming back, but how much it helps any one woman depends mostly on how high her risk was in the first place. Large trials and combined analyses of many thousands of women show that around five years of hormone therapy clearly reduces the risk of recurrence and of dying from breast cancer, and that the protection continues for years after the tablets stop. For women past menopause, aromatase inhibitors such as anastrozole reduce recurrence somewhat more than tamoxifen. To make sense of the numbers you will hear, it helps to separate relative and absolute benefit. A relative benefit is the share of risk a treatment removes, for example cutting risk by a third. An absolute benefit is how many women out of a hundred actually avoid a recurrence because of the treatment. The same relative cut gives a large absolute gain when the starting risk is high, such as a large tumour or cancer in several lymph nodes, and a smaller absolute gain when the starting risk is low, such as a small, low-grade, node-negative tumour. So two women taking the same tablet can gain very different amounts. Anastrozole also lowers the chance of a new cancer in the other breast, and in some high-risk women it is used to reduce the risk of a first breast cancer. Your oncologist can use tools such as Predict Breast to estimate what anastrozole is likely to offer someone with your age and cancer details.

The benefit is real and lasts

Hormone therapy reduces recurrence, and protection carries on after treatment ends.

Your starting risk shapes your gain

Higher-risk cancers gain more, in absolute terms, from the same tablet.

Ask for your own estimate

Your oncologist can work out a likely benefit using your own reports.

Benefit figures are useful for decisions, but they have firm limits.

No one can tell whether it helped you

If the cancer never returns, there is no way of knowing whether it would have returned without anastrozole.

Tools are estimates

Predict Breast and similar tools are built mainly from Western data and may be less exact for Indian women or unusual cancers.

Benefit depends on taking it

Trial figures assume women took their tablets. Frequent missed doses or stopping early reduce the gain.

What this page cannot tell you

It cannot give your personal figures. Your oncologist can, using your pathology report.

Anastrozole is used in other settings, and benefit is measured differently in each.

Lowering risk in high-risk women

In a large prevention trial of women past menopause at raised risk, anastrozole reduced the number of new breast cancers by roughly half, with the effect lasting after treatment stopped. Side effects mean it is only offered after careful discussion.

Advanced breast cancer

When cancer has spread, benefit is measured as the time the cancer stays under control. Combining anastrozole with a targeted tablet such as ribociclib, palbociclib or abemaciclib has lengthened that time in trials.

Weighing it up

Where the likely gain is small, side effects deserve more weight. Where it is large, extra support to continue is worthwhile.