OREANDA-NEWS. Medivation, Inc. (Nasdaq: MDVN) and Astellas Pharma Inc. (Tokyo: 4503), announced today the presentation of Stage 1 and preliminary Stage 2 data from a Phase 2 study evaluating the use of enzalutamide as a single agent for the treatment of advanced androgen receptor positive (AR+), triple negative breast cancer (TNBC). Data was presented at the 37th Annual San Antonio Breast Cancer Symposium.

Title:  Stage 1 Results from MDV3100-11:  A 2-Stage Study of Enzalutamide (ENZA), an Androgen Receptor (AR) Inhibitor, in Advanced AR+ Triple-Negative Breast Cancer (TNBC) (Abstract # P5-19-09).

Patients with any amount of AR staining by immunohistochemistry could be enrolled in the study (n=42 in Stage 1, n=118 in total). The primary endpoint was clinical benefit rate, defined as the portion of Evaluable patients (?10% AR staining in tumor cells and a post-baseline assessment) who had a complete response, partial response, or stable disease for at least 16 weeks. There was no limit to prior therapy.  In Stage 1, 26 of the 42 enrolled women comprised the Evaluable population.

  • In the 26 Evaluable women, the primary endpoint was achieved in 42% (11 of 26) including 1 partial response in a patient with measurable disease and 1 complete response in a patient with non measurable disease. Clinical benefit rate ?24 weeks was achieved in 35% (9 of 26). 
  • The clinical benefit rate > 16 weeks in Stage 1 was sufficiently high to enable both the expansion into Stage 2 and early rejection of the null hypothesis.
  • While data are not yet mature (anticipated 2015), 1 additional complete response and 3 additional partial responses have been observed to date in the additional 76 patients enrolled following Stage 1, for a total of 6 complete or partial responses in both Stages as of November 10, 2014. 

The most common adverse events reported in the Stage 1 intent to treat population (n=42)  were fatigue (36%), nausea (33%), diarrhea (21%), decreased appetite (21%), back pain (14%), headache (14%), hot flush (12%), insomnia (12%), vomiting (12%), pain (12%) and constipation (12%). To date, the safety and tolerability profile of the additional patients enrolled in Stage 2  are consistent with the profile seen in Stage 1. Patients will continue to be monitored for safety. 

“The  combined results from Stage 1 and 2 suggest that enzalutamide may provide a potential benefit to women with advanced androgen-receptor positive, triple-negative breast cancer,” said Tiffany A Traina, M.D., primary investigator of the study and medical oncologist, Memorial Sloan Kettering Cancer Center.  “This is encouraging for patients with this type of breast cancer because it is a particularly challenging subtype of the disease, for which the only available treatment option is chemotherapy.”

Androgen-receptor positive TNBC  is a recently-identified subtype that can express high levels of the androgen receptor. This Phase 2 study of single agent enzalutamide is the largest to date in patients with AR+ TNBC and the first to report objective responses to a hormonal therapy. 

TNBC remains an area of significant unmet medical need. Currently, there are no approved targeted therapies for these patients, who are typically treated with multiple regimens of chemotherapy.

About the Phase 2 Study

The Phase 2 open label, single-arm study was initiated in June 2013 and completed enrollment in July 2014.  118 patients were enrolled in 2 Stages at sites in the United States, Canada and Europe.  The primary endpoint of the trial is clinical benefit rate, defined as the proportion of patients with a best response of complete response, partial response or stable disease at ? 16 weeks. All patients receive enzalutamide at a dose of 160 mg to be taken orally once daily.