The drug anastrozole is effective in treating an early form of breast cancer, according to a clinical trial. The results of the IBIS-II DCIS trial show that anastrozole is as effective as tamoxifen for this type of breast cancer and could offer a new treatment option for post-menopausal women.
Ductal carcinoma in situ (DCIS) is described as a very early form of breast cancer, where cancer cells are present in milk ducts, but have not spread to the surrounding breast tissue. It is estimated that approximately a fifth of all screen-detected breast cancers are DCIS, with around 4,800 people diagnosed with DCIS in the UK each year.
"We found that anastrozole and tamoxifen had similar overall efficacies, with slightly better outcomes for those who took anastrozole. But more importantly, because of their very different side-effects, anastrozole can be offered as an alternative for patients who may not tolerate tamoxifen as well or have previous illnesses making tamoxifen unsuitable.
The study looked at 2,980 postmenopausal women with DCIS in 14 countries, who were either given anastrozole or tamoxifen for five years after surgery. After a median follow-up of 7.2 years, 144 participants developed breast cancer, and 69 died, of which four were due to breast cancer.
The groups had a similar number of cases of the disease recurring, whether they took tamoxifen or anastrozole. Those who took anastrozole had an 11 per cent lower rate of recurrence of DCIS or invasive cancer than those who took tamoxifen, but this difference was not significant.
The women in the two groups had different side effects. Women who took anastrozole experienced fewer womb and ovarian cancers and non melanoma skin cancers, and fewer deep vein thromboses and gynecological issues, compared with those who took tamoxifen. However, more strokes, fractures and musculoskeletal issues were seen among those receiving anastrozole.
The trial was limited by its lower-than-expected event rate, which adds uncertainly about the lack of statistical significance of some of the small differences seen. The authors say it is too early to assess the effect of these treatments on mortality, and long-term follow-up and further research is planned to study these issues.