Cancer Research has published the results of a population-based case-control that aimed to assess the association between hormonal treatment of oestrogen receptor positive tumours with tamoxifen and the development of primary oestrogen receptor negative tumours. The results of this study have been reported in the general media (BBC).
The study analysed data from 367 women who developed a receptor positive tumour in one breast followed by a receptor negative tumour in the other breast some time later. These data were compared with 728 control case patients who did not develop a second tumour. Telephone interviews and assessment of medical records collected data on adjuvant hormonal therapy, other treatments and breast cancer risk factors.
Users of adjuvant hormonal therapy for 5 years or more were found to have a 60% reduction in the risk of developing a receptor positive tumour in the other breast but a 440% increased risk of developing a receptor negative tumour. Tamoxifen use for less than 5 years was not associated with an increased risk.
The authors conclude that "oestrogen-blocking drugs like tamoxifen have important clinical benefits" but that these drugs have risks and an increased risk of receptor negative cancer may be one of these risks. It is also stated that the benefits of this therapy are well established and doctors should continue to recommend hormonal therapy for breast cancer patients.
Cancer Research UK have also offered reassurance in light of these results stating that "the benefits of taking hormone-blocking drugs, such as tamoxifen, after their first diagnosis of breast cancer far outweigh any potential risks".
Action: Clinicians should be aware of this study and its coverage in the media coverage. Patients taking adjuvant hormonal therapies should be reassured and encouraged to continue with treatment.