A diagnosis of cancer could be expected to concentrate the patient's mind on the best way to recovery. It is alarming, therefore, to discover that as many as half of breast cancer patients prescribed tamoxifen, the most widely-prescribed drug for breast cancer, are risking their lives by failing to take it for the full five-year course of treatment. A study carried out on more than 2000 women in Tayside found that 90% took it daily as prescribed for the first year, but that adherence rates dropped off progressively until 51% had stopped taking it after five years. The findings are in line with other research into compliance with prescription regimes, but the significance of the Dundee results is that for the first time they have quantified the increased risk of death for those who flout their doctor's instructions about how to take their medicine. In this case, women who miss at least one tamoxifen tablet every five days increase their risk of dying by 10%.

Tamoxifen is estimated to have saved the lives of 30% of all women diagnosed with breast cancer since it was developed more than 30 years ago. Although the incidence of breast cancer has soared by 80% in Britain in that time, survival rates have increased and previous studies have shown that women receiving tamoxifen therapy for less than five years have significantly higher rates both of recurrence of breast cancer and death.

The most likely cause for missing tablets or stopping taking them completely is the unpleasant side-effects. They include menopause-like symptoms including hot flushes, depression and an increased risk of deep-vein thrombosis and uterine cancer. The finding of the Tayside study that younger women were more likely to stop taking the medication early suggests that they are more likely to find these side-effects unacceptable. In addition, the fact that there was no difference in compliance rates between rich and poor indicates that the cost of prescription charges (which have since been reduced for cancer patients) was not significant, reinforcing the probability of side-effects being the major deterrent. That makes it essential that patients are continuously monitored. After a number of high-profile campaigns by individuals, including for the alternative breast cancer treatment, herceptin, there will be increasing demands for new and more expensive anti-cancer drugs to be licensed for use in the NHS. That makes it all the more important that best use is made of treatment which is already available. Yet it is clear from this survey, which was carried out using prescription records, that some patients are falling below the radar.

With 4000 women a year diagnosed with breast cancer in Scotland, there are now large numbers on regular repeat prescriptions for tamoxifen, but with computerised records it should be possible for GP practices to monitor take-up at regular intervals and follow up any unexplained gaps. In some cases it may be that an adjustment of dosage is required, in others a proper explanation of the need to continue taking the medication regularly. When the prognosis for surviving breast cancer is good and getting better, patients should not be risking an unnecessarily early death.