The primary purpose of this study is to measure the association between baseline expression of the senescence effector protein p16INK4a and myelosuppression due to chemotherapy in patients with breast cancer. Patients with Stage I-IV breast cancer will be included and myelosuppression will be assessed after the first cycle of chemotherapy via measurement of an absolute neutrophil count (ANC) measured one time between days 7-11 post cycle one. Study subjects will also be asked to complete a brief health behaviors questionnaire to gather information on other relevant variables.

Inclusion Criteria:

• ≥ 18 years of age;
• Histologically confirmed Stage I-IV breast cancer;
• ECOG Performance Status 0-3;
• Scheduled to start a new course of chemotherapy in the neo-adjuvant, adjuvant or metastatic setting for newly diagnosed or recurrent disease;
• Growth factors, e.g., filgrastim, pegfilgrastim, are allowed, but their dose and duration will be tracked.
• Absolute Lymphocyte Count (ALC) > 500 cells/μL as determined by routine CBC with differential;
• Signed, IRB approved written informed consent.

Exclusion Criteria:

• Presence of acute, active infection;
• History of clonal bone marrow disorder (i.e., myelodysplastic or myeloproliferative disorder, acute or chronic leukemia);
• Other co-morbid illness which would impair ability to participate in the study;
• Concurrent experimental therapy (Note: concurrent biologic therapy IS permitted, provided it is not experimental).
• Prior or current receipt of histone deacetylase (HDAC) inhibitors

Breast cancer patients at UNC North Carolina Cancer Hospital and other participating sights.