Inclusion Criteria:

          -  Patients must be able to swallow and retain oral medication

          -  Patients must be ≥ 18 years of age

          -  Patients must be post-menopausal

          -  Patients must have ECOG performance status 0 - 1

          -  Patients must have clinical stage IV or inoperable locoregional recurrent invasive
             mammary carcinoma that is ER+ and/or PgR+ (≥ 1% positive stained cells) by
             immunohistochemistry (IHC), HER2-negative (by IHC or FISH, per ASCO guidelines) and
             FGFR1, FGFR2, FGFR3 or FGFR4 amplified (may be determined by local assessment through
             either targeted capture next generation sequencing (NGS), plasma cell-free tumor [cf]
             DNA or FISH*)

          -  Patients must have evaluable (may have either measurable or non-measurable) disease

          -  Patients must have available tissue for FGFR determination

          -  Patients must have adequate hematologic, hepatic and renal function.

        Exclusion Criteria:

          -  Prior use of an FGFR inhibitor

          -  More than 2 lines of chemotherapy in the metastatic setting. No limit on endocrine
             therapy lines. Prior exposure to CDK4/6 inhibitor acceptable.

          -  Radiation therapy ≤ 2 weeks prior to study entry. Patients who have received prior
             radiotherapy must have recovered from toxicity (≤ grade 1) induced by this treatment
             (except for alopecia)

          -  Prior cancer therapy (except for endocrine therapy) must have been discontinued for 1
             week prior to initiation of study drugs

          -  Concurrent anti-cancer therapy other than the ones specified in the protocol is not
             permitted during study participation. Bisphosphonates or denosumab are allowed

          -  Current use of any of the prohibited drugs

          -  Herbal preparations are not allowed throughout the study, and should be discontinued
             14 days prior to initiation of study treatment

          -  Any corneal or retinal abnormality likely to increase the risk of eye toxicity, such
             as current corneal pathology such as keratitis, keratoconjunctivitis, keratopathy,
             corneal abrasion, inflammation or ulceration, uncontrolled glaucoma despite standard
             of care therapy, diabetic retinopathy with macular edema, known active wet,
             age-related macular degeneration (AMD), or known central serous retinopathy (CSR) or
             retinal vascular occlusion (RVO)

          -  Malabsorption syndrome significantly affecting gastrointestinal function

          -  Ongoing or active infection requiring parenteral antibiotics

          -  Impairment of lung function (COPD > grade 2, lung conditions requiring oxygen therapy)

          -  Symptomatic congestive heart failure

          -  Unstable angina pectoris, angioplasty, stenting, or myocardial infarction within 6
             months

          -  Clinically significant cardiac arrhythmia (multifocal premature ventricular
             contractions, bigeminy, trigeminy, ventricular tachycardia that is symptomatic or
             requires treatment [National Cancer Institute -Common Terminology Criteria for Adverse
             Events, Version 4.03, grade 3]

          -  QTcF ≥ 480 msec on screening EKG

          -  Known history of clinically significant QT/QTc prolongation or Torsades de
             Pointes(TdP)

          -  ST depression or elevation of ≥ 1.5 mm in 2 or more leads

          -  Diarrhea of any cause ≥ CTCAE grade 2

          -  Psychiatric illness/social situations that would compromise patient safety or limit
             compliance with study requirements including maintenance of a compliance/pill diary
             lSymptomatic brain metastases (patients with a history of brain metastases must be
             clinically stable for more than 4 weeks from completion of radiation treatment and be
             off steroids)

          -  Known history of chronic liver or chronic renal failure