Testing the Use of Fulvestrant and Binimetinib Targeted Treatment for NF1 Mutation in Hormone Receptor-Positive Metastatic Breast Cancer (A ComboMATCH Treatment Trial)

PRIMARY OBJECTIVES: I. To determine whether the combination of fulvestrant and binimetinib improves progression-free survival (PFS) compared to treatment with fulvestrant alone in patients not previously treated with fulvestrant. (Cohort 1) II. To determine whether overall response rate (ORR) within 4 months in patients who have previously progressed on a fulvestrant-containing regimen is greater than 10%, as a historical comparison, when these patients receive combination fulvestrant and binimetinib therapy. (Cohort 2) SECONDARY OBJECTIVES: I. To estimate ORR at any time after the start of the treatment for Cohort 2 and separately for the two arms in Cohort 1. II. To estimate PFS distribution in Cohort 2. III. To estimate clinical benefit rate separately for the two arms in Cohort 1 and Cohort 2. IV. To determine the safety and toxicity profile in both cohorts. V. To estimate the overall survival (OS) in both cohorts. VI. Collect tissue and provide it to the ComboMATCH Registration Protocol to assess concordance between the diagnostic tumor mutation profile generated by the Designated Laboratories, the pre-treatment biopsy mutation profile, and the pre-treatment circulating tumor deoxyribonucleic acid (DNA) (ctDNA) mutation profile from plasma, as described in ComboMATCH Registration Protocol. For this treatment substudy, the outcome objective will be to report the proportion of cases providing sufficient tissue for that integrated scientific activity in the ComboMATCH Registration Protocol. EXPLORATORY BIOMARKER OBJECTIVES: I. To analyze the cell-free (cf)DNA at progression to determine the changes in cfDNA profile in order to understand blood-based mutation dynamics. II. To analyze RNAseq at progression to determine potential pathways that are altered that may contribute to the sensitivity/resistance. III. To discover/detect novel biomarkers using microscaled proteogenomics by analyzing the proteins and phosphor-proteins along with genomics to determine potential pathways that may correlate with the response to the combination treatment. IV. To detect the loss of NF1, using immunohistochemistry staining to precisely measure the level of the NF1 protein. V. To determine the variant allele frequency (VAF) of mutant NF1 measuring by using droplet digital polymerase chain reaction (ddPCR) for the targeted NF1 gene level. OUTLINE: Patients who are fulvestrant naive are assigned to Cohort I, while patients who are fulvestrant resistant are assigned to Cohort II. COHORT I: Patients are randomized to 1 of 2 arms. ARM I: Patients receive fulvestrant intramuscularly (IM) on day 1 and day 15 of cycle 1 and day 1 of subsequent cycles and binimetinib orally (PO) twice daily (BID) on days 15 to 28 of cycle 1 and day 1 through 28 of subsequent cycles. Cycles repeat every 28 days in the absence of disease progression or unacceptable toxicity. Patients also undergo a computed tomography (CT), magnetic resonance imaging (MRI), or bone scan, echocardiography (ECHO) or multi-gated acqusition scan (MUGA), and tumor biopsy, as well as possible blood sample collection during screening and on study. ARM II: Patients receive fulvestrant IM on day 1 and day 15 of cycle 1 and day 1 of subsequent cycles. Cycles repeat every 28 days in the absence of disease progression or unacceptable toxicity. Patients who progress on fulvestrant alone may migrate to cohort II if they meet the migration eligibility criteria. Patients not willing to migrate to cohort II will have further therapy at the investigator's discretion. Patients undergo a CT, MRI, or bone scan and tumor biopsy, as well as ECHO or MUGA and possible blood sample collection during screening and on study. COHORT II: Patients receive fulvestrant IM on day 1 of each cycle and binimetinib PO BID on days 15-28 of cycle 1 and day 1 through 28 of subsequent cycles. Cycles repeat every 28 days in the absence of disease progression or unacceptable toxicity. Patients undergo a CT, MRI, or bone scan, ECHO or MUGA and tumor biopsy, as well as possible blood sample collection during screening and on study. Upon completion of study treatment patients are followed up every 6 months for 5 years.