ANZ 02P2 / International Breast cancer Intervention Study: IBIS-II DCIS

INTERVENTION: Anastrozole 1 mg + Tamoxifen placebo (lactose pill). All treatment will be on a daily basis for 5 years and all women will take 2 tablets/day orally. CONDITION: Increased breast cancer risk PRIMARY OUTCOME: To compare side effect profiles of tamoxifen and anastrozole. To determine if anastrozole is at least as effective as tamoxifen in local control and prevention of contralateral disease in women with unilateral locally excised ER and/or PgR +ve DCIS. SECONDARY OUTCOME: To compare the effectiveness of tamoxifen and anastrozole according to the receptor status of the primary or recurrent cancer. To examine the effect of tamoxifen and anastrozole on other cancers, cardiovascular disease, fracture rates, and non‐breast cancer deaths. To examine the effect of tamoxifen vs anastrozole on breast cancer mortality. To examine the rate of breast cancer recurrence and new contralateral tumours after cessation of tamoxifen or anastrozole. To examine tolerability and acceptability of side effects experienced by women on the trial. INCLUSION CRITERIA: 1. All women must be postmenopausal. 2. Hormone replacement therapy must have stopped at least 8 weeks prior to randomisation.3. Locally excised unilateral DCIS diagnosed within the last 6 months. Oestrogen receptor and/or progesterone receptor (ER and/or PgR) status of the DCIS must be known and greater than 5% positive cells.4. A baseline bone mineral density scan within the last 2 years (DXA either of hip, lumbar spine or forearm) will be required for all women. A spinal x‐ray within the last 2 years to rule out low trauma vertebral fractures will also be required.5. A bilateral mammogram must have been taken within the last year.6. Fully informed consent must be provided.7. Women treated by mastectomy will not be eligible for this trial, but may enter the parallel IBIS II (Prevention) trial.8. Must be accessible for treatment and follow up via a participating institution. 9. Participants from the IBIS‐I clinical trial who have been off trial therapy for at l