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.