Study of Infigratinib in Combination With Tamoxifen in Hormone Receptor Positive, HER2 Negative, FGFR Altered Advanced Breast Cancer

Primary Objective: Determine the maximum (no greater than 125 mg) dose of infigratinib used in combination with the FDA-approved dose and schedule of tamoxifen (Cohort 1) in terms of the number of dose-limiting toxicities observed in the first 2 cycles of therapy in subjects with hormone receptor-positive, HER2-negative advanced breast cancer. Secondary Objective: * Estimate the incidence of treatment-emergent adverse events (serious and non-serious). * Estimate the objective tumor response rate (ORR) in subjects with measurable disease. * Estimate the progression-free survival (PFS). * Estimate the durable clinical benefit rate.