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Anastrozole Shows Promise for Breast Cancer Chemoprevention: Presented at SGOC
By Chris Berrie
St. GALLEN, SWITZERLAND -- February 17, 2004 -- The aromatase inhibitor anastrozole may well prove to be more promising than the selective estrogen receptor modulators (SERMs) for prevention of breast cancer in postmenopausal women at high risk of developing the disease.
The findings were presented here on February 13th at the 3rd International St. Gallen Oncology Conference: Controversies in Tumor Prevention and Genetics 2004.
From their recent overview of all tamoxifen trials, Jack Cuzick, MD, Head, Mathematics, Statistics and Epidemiology Group, Imperial Cancer Research Fund, London, United Kingdom, said that they came to the conclusion that about one third of breast cancer cases are preventable by using tamoxifen.
However, on the topic of anastrozole, Dr. Cuzick said, "The only data that has really come through from aromatase inhibitors is the studies of the ATAC trial that has given us a lot of information about the side effects [of these agents]." Indeed, he said that the reduction of new contralateral tumours seen in that trial (OR, 0.62, P = .062; versus tamoxifen) would indicate that the efficacy of anastrozole will be better than tamoxifen: "Instead of about a 50% reduction in ER [estrogen receptor]-positive tumours, we might hope to see a 75% reduction."
Dr. Cuzick highlighted the decreases in the main tamoxifen-induced side effects that were achieved by anastrozole use -- endometrial cancer -77% (P = .03), cerebrovascular events -50% (P = .0006) and thromboembolic events -40% (P = .0006), although this might be at the expense of bone incidents. "So the [incidence of bone] fractures is the issue we have to deal with, and we are looking very intensively at using bisphosphonates to actually control that at the same time," he added.
The International Breast Cancer Intervention Study II (IBIS II) study will do just that, compare anastrozole both against placebo in 6,000 high-risk postmenopausal women, and against tamoxifen in a further 4,000 postmenopausal women with locally excised ER-positive ductal carcinoma in situ. The study also has a detailed substudy built in, which will evaluate the use of the bisphosphonate risedronate in 1,000 women with osteopenia.
The recruitment for IBIS-II has started and will continue over the next 3 to 4 years, to complete the full recruitment of 10,000 women.
"[The study] is running in 5 countries now, and we expect it to run in about 15 countries around the world; almost everywhere except Africa and North America," Dr. Cuzick said. This includes 5 years of active treatment, so the results should be available in about 9 years, he added. "So maybe the most appropriate strategy will be an aromatase inhibitor plus a bisphosphonate, thus dealing with both osteoporosis and breast cancer at the same time," Dr. Cuzick said.
[Study title: Aromatase inhibitors in breast cancer prevention: The IBIS II Trial. Abstract S17]
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