Surprise result regarding osteoporotic fracture risk post anastrazole treatment

Delegates at the Australia and New Zealand joint scientific meeting for the Medical Oncology Group of Australia and the Faculty of Radiation Oncology, were given some good news yesterday when Professor Alan Coates presented the mature data from the ATAC study.

The superiority of aromatase inhibitors (AIs) compared to tamoxifen is established in hormone receptor post menopausal women but it has long been known that the AIs, anastrazole, letrozole and exomastane, have the unwanted side effect of bone loss leading to osteoporosis and increased fracture rates.

Professor Coates demonstrated the prolonged benefit of 5 years of hormonal therapy for HR positive breast cancer and found this benefit to persist 4 years after treatment was completed.

The data from the ATAC study confirmed the higher fracture rate in patients being treated with anastrozole during the treatment phase (relative risk 1.55, anastrozole vs. tamoxifen) but somewhat surprisingly risk of fracture normalised within 12 months of stopping therapy.

Professor Coates did however caution the audience that this finding may in some part be due to less stringent follow-up on the post treatment phase which could result in under-reporting of post-treatment fractures. The same would also be true for under-reporting of fractures on tamoxifen however.

Further debate on this topic is inevitable as a significant proportion of medical oncologists feel that optimum treatment is a combination of tamoxifen for 2 years followed by 3 years of aromatase inhibitor.