Oral Presentation Joint 2016 COSA and ANZBCTG Annual Scientific Meeting

Breast density change: Towards tailoring of adjuvant endocrine therapy (#120)

Andrew Redfern 1
  1. University of Western Australia, Applecross, WA, Australia

Of the estimated 16084 breast cancer diagnoses predicted to occur in Australia in 2016, over two thirds will be estrogen and or progesterone receptor positive and thus candidates for adjuvant endocrine therapy. Assuming a mean five year treatment period places around 50,000 women on such agents currently. Despite this volume of patients , the long duration of treatment and the potential toxicities, no tools are currently available to assess, either before or during treatment, the likelihood of benefit on these medications beyond the occurrence or otherwise of disease relapse.

Mammographic breast density (MBD) has repeatedly been shown to be a risk factor for initial breast cancer. In smaller series in the adjuvant setting higher initial MBD has also been correlated with local disease relapse. Longitudinal studies in the preventative setting have demonstrated that MBD frequently falls on anti-estrogens, particularly tamoxifen, relative to placebo. This introduces the possibility that MBD fall on an anti-estrogen may predict eventual adjuvant efficacy, allowing a change to a potentially more efficacious agent where lack of MBD change predicts the absence of benefit from the first drug employed.

The IBIS 1 study demonstrated that the primary preventative benefits of tamoxifen were almost entirely confined to those participants experiencing significant MBD reduction. Consequently, a number of retrospective cohort studies have demonstrated similar correlations in the adjuvant setting after breast cancer surgery. An overview of these studies will be presented outlining the predictive potential, limitations within patient groups by demographics and differential results by anti-estrogen class. Further, a way forward will be discussed that could bring MBD change into routine clinical use as a biomarker of anti-estrogen efficacy. This will include consideration of the retrospective analysis of existing anti-estrogen trial cohorts and the consequent inception of prospective studies.