Palbociclib / Letrozole or Fulvestrant in African American Women With HR+ HER2- Breast Cancer

The study is designed to assess the rate of completion of planned oncology therapy in the absence of a hematological event defined as episodes of febrile neutropenia and treatment discontinuation due to neutropenia. A completion rate of 80% is considered of clinical relevance as to benefit breast cancer patients who are at a higher risk of having ethnic neutropenia where as a completion rate of 60% is considered poor and to justify additional safety studies. A two stage design with a total of 35 patients is used to test if the completion rate is at least 80% versus if it is below 60% with 80% power at a significance level of 5%. An exact confidence interval of the completion rate will be calculated. Investigators estimate there will be no more than a 10% rate of febrile neutropenia. Due to the small sample size, the analysis of secondary endpoints will be descriptive and will not include specific hypothesis testing.