Portman, DJ

Abstract Background: Estrogen receptor gene (ESR1) mutations present in breast cancer patients are associated with resistance to endocrine therapy and worse patient outcomes. Recent findings suggest ESR1 mutations are present in up to 40% of metastatic breast cancer (mBC) patients' tumors. The objective of this study was to evaluate the perceptions of precision medicine and biomarker testing specific to ESR1 mutations among medical oncologists. Methods: Ten 60-minute web-assisted, telephone interviews were conducted with medical oncologists. Each physician was prescreened prior to being interviewed to ensure board certification and practice experience between 2 and 35 years. Each participant spent greater than 30% of their time on direct patient care and managed the treatment of more than 30 different cancer patients per month, with a minimum of 15 breast cancer patients, including at least five who had metastatic breast cancer and at least one patient with an ESR1 mutation. Results: A 10-20% prevalence of ESR1 mutation was estimated by the oncologists. However, the practitioners did accept the possibility of a 40% prevalence. Physician knowledge of ESR1 mutations included the relationship between ESR1 mutations and efficacy of endocrine therapies and its association with poorer outcomes. None of the medical oncologists interviewed were highly satisfied with the existing armamentarium of treatments for patients with an ESR1 mutation. In general, the interview participants were highly comfortable ordering ESR1 companion diagnostics to test for an ESR1 mutation, pending viable treatment options are available. Nonetheless, most physicians will wait until the patient has progression of disease before ordering a biomarker test. Several areas of unmet need in the mBC arena were offered by the survey participants, including more efficacious hormonal options for later-line therapies, better durability of remission, improved drug tolerability profiles, and lower treatment costs. Conclusion: Most oncologists acknowledged that personalized treatment is beneficial because it allows for better efficacy than a “one size fits all” approach. The study results also suggest that there are few barriers and drawbacks to the use of personalized medicine in the mBC arena, as most physicians expect precision medicine to account for the majority of advances in breast cancer treatments in the foreseeable future. Support: Sermonix Pharmaceuticals Citation Format: Goldfarb SB, Goetz MP, Plourde PP, Attias E, Portman DJ. A preliminary assessment of knowledge, attitudes, and awareness surrounding ESR1 mutations and biomarker testing amongst medical oncologists [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-11-11.

Abstract Endocrine based therapy is the standard treatment for estrogen receptor positive (ER+) MBC. Agents targeting the ER pathway including aromatase inhibitors (AIs), fulvestrant and tamoxifen along with CDK 4/6 inhibitors are considered standard for first and 2nd line treatment. However, endocrine resistance develops in nearly all patients and the optimal systemic therapy after progression on a CDK 4/6 inhibitor is unknown. Lasofoxifene is a third generation SERM previously investigated for the treatment of osteoporosis and vulvo-vaginal atrophy (VVA). In a large phase 3 trial evaluating the efficacy of lasofoxifene for the postmenopausal treatment of osteoporosis, lasofoxifene significantly reduced the incidence of ER+ breast cancer. Further unpublished preclinical data have demonstrated significant in vitro and in vivo efficacy in non-clinical breast cancer models including models with and without ESR1 mutants. Moreover, lasofoxifene significantly reduced metastases in ESR1 mutated models. These non-clinical and clinical data provide a strong rationale to pursue a phase 2 clinical trial in women with ER+, ESR1 mutated MBC. This open-label, multi-center study will compare the efficacy and tolerability of lasofoxifene (5 mg orally daily) to fulvestrant (IM 500 mg D1,15,29 and then q30 D) in a 1:1 randomization. Inclusion criteria include postmenopausal women with ER+ advanced breast cancer; progression on a non-steroidal AI in combination with a CDK 4/6 inhibitor; and a known ESR1 mutation. Approximately 90 patients with measurable or evaluable disease (i.e. bone only) will be recruited to have at least 40 patients per treatment arm. The primary endpoint will be progression free survival (PFS) with secondary endpoints of objective response rate (ORR), clinical benefit rate (CBR), duration of response (DoR) and time to response (TTR). It is assumed that lasofoxifene will double the median PFS compared to fulvestrant in this ESR1 mutation patient population for a hazard ratio 0.5 and a power of 89% to reach a 1-sided p of <0.05. The study will commence in 4Q2018 and will complete recruitment in 1 year. It is anticipated that 25-30 centers in the US will be participating. Citation Format: Plourde PV, Schwartzberg LS, Greene GL, Portman DJ, Komm BS, Jenkins SN, Liu P-Y, Portman MD, Goetz MP. An open-label, randomized, multi-center phase 2 study evaluating the activity of lasofoxifene relative to fulvestrant for the treatment of postmenopausal women with locally advanced or metastatic ER+/HER2 - breast cancer (MBC) with an ESR1 mutation [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT1-01-02.