The purpose of this study is to evaluate the effect of food on the pharmacokinetics (PK) of the experimental drug, entinostat, in women with breast cancer and men and women with non-small cell lung cancer. The safety and tolerability of entinostat will also be evaluated when entinostat is given by itself as well as with the approved drugs, exemestane (Aromasin®) or erlotinib (Tarceva®). A biomarker (chemical "marker" in the blood/tissue that may be related to your response to the study drug) will also be tested.

This is Phase 1, randomized, open-label, study of entinostat. The study is designed to evaluate any food effect on the pharmacokinetics of entinostat.

Patients will be randomized to receive entinostat with or without food on Cycle 1 Day 1 (C1D1). Patients randomized to receive entinostat with food on C1D1 will receive a second dose of entinostat without food on Cycle 1 Day 15 (C1D15). Patients randomized to receive entinostat without food on C1D1 will receive a second dose of entinostat with food on C1D15. Each cycle in the study will be for 28 days duration. Blood samples will be obtained pre-dose and serial blood samples will be taken after each dose to assess pharmacokinetics. For Cycle 2 and all subsequent cycles, all patients will continue to receive entinostat on Days 1 and 15 of each cycle. Those with breast cancer will also receive exemestane orally once daily starting on Cycle 2 Day 1. Those with NSCLC will also receive erlotinib starting on Cycle 2 Day 1.

Patients will be assessed at screening and at pre-prescribed times during study enrollment using standard assessments. Patients will also be assessed for tumor response after each 2 cycles. Patients will continue receiving study treatment until tumor progression or adverse events occur which necessitate discontinuing therapy as determined by the Investigator.

Inclusion Criteria:

Breast Cancer Patients Only

• Postmenopausal female patients
• Histologically or cytologically confirmed ER+ breast cancer at initial diagnosis and now has current disease progression and is a candidate to receive exemestane

NSCLC Patients Only:

• Cytologically or histologically confirmed NSCLC of stage IIIb or IV
• Received 1 to 2 prior chemotherapy or chemoradiotherapy regimens for advanced NSCLC (excluding erlotinib and valproic acid) and now has disease progression and is a candidate to receive erlotinib

All Patients:

• Age ≥ 18 years
• Patient must have the following laboratory parameters at study screening: Hemoglobin ≥ 9.0 g/dL; unsupported platelets ≥ 100.0 10-9/L; ANC ≥ 2.0 x 10-9/L; Creatinine less than 2.5 times the upper limit of normal for the institution; AST and alanine transaminase (ALT) < 2.5 times the upper limit of normal for the institution
• Patients may have a history of brain metastasis as long as certain criteria are met

Exclusion Criteria:

• Pregnant or lactating women
• Patient has rapidly progressive or life-threatening metastases.
• Patient has had previous treatment with entinostat or any other HDAC inhibitor including valproic acid
• Patient has a concomitant medical condition that precludes adequate study treatment compliance or assessment, or increases patient risk in the opinion of the investigator, such as but not limited to:

MI or arterial thromboembolic events within 6 months, or experiencing severe or unstable angina, New York Heart Association (NYHA) Class III or IV disease and a QTc interval > 0.47 seconds.

Uncontrolled heart failure or hypertension, uncontrolled diabetes mellitus, uncontrolled systemic infection.

• Patients with another active cancer (excluding adequately treated basal cell carcinoma or cervical intraepithelial neoplasia [CIN / cervical carcinoma in situ] or melanoma in situ). Prior history of other cancer is allowed, as long as there is no active disease within the prior 5 years.