The majority of women diagnosed with breast cancer are post-menopausal, of which up to 75% are estrogen (ER) and/or progesterone receptor (PR) positive. Even in pre-menopausal breast cancer over half of all patients will have expression of these hormone receptors. Thus therapeutic strategies targeting the estrogen receptor or its ligand are the most common treatment offered in breast cancer. Despite substantial benefits now demonstrated with selective estrogen receptor modulators (e.g. tamoxifen) and aromatase inhibitors (e.g. anastrazole, letrozole and exemestane), a significant proportion of patients will still unfortunately have or develop resistance to these hormonal therapies.
Despite approximately two-thirds of patients who are prescribed fulvestrant following prior hormonal agents not benefiting from this therapy, clinicians are still offering this option to all suitable women because of the lack of a better means of identifying the individual responders.
To assess whether the recommended treatment is beneficial to a specific individual, the disease burden is assessed before and following treatment. Conventional imaging techniques such as the bone scan or computerized tomography (CT) can take several months to show a successful response to treatment. Positron emission tomography (PET) can improve the evaluation of women with breast cancer by providing an accurate assessment of the extent of disease and unique information about tumor biology such as metabolic activity.
