• Disease control rate (complete response, partial response, or stable disease for at least 3 months) [ Time Frame: 3 months ] [ Designated as safety issue: No ]
  

• Progression-free survival rate at 2 months [ Time Frame: 2 months ] [ Designated as safety issue: No ]
  
• Progression-free survival rate at 4 months [ Time Frame: 4 months ] [ Designated as safety issue: No ]
  

INCLUSION:

1. Cytologically or histologically confirmed NSCLC of stage IIIb (pleural effusion) or IV
2. Disease is progressing (either no response to treatment or subsequent relapse after an objective response) on erlotinib treatment, based on at least 2 scans (the last being within 4 weeks of study enrollment and can serve as the baseline scan for the patient's screening into the study )
3. Recovered from any toxicity associated with the most recent cancer treatment (no greater than grade 1 toxicity on CTCAE scale or to prior baseline condition)
4. At least 1 measurable lesion ≥ 20mm by conventional CT scan or ≥ 10mm by spiral CT scan
5. ECOG performance score of 0, 1, or 2 and life expectancy of at least 3 months
6. Paraffin-embedded tumor specimen available for correlative studies
7. Male or female over 18 years of age
8. Hemoglobin ≥ 9.0 g/dL; platelets ≥ 75 x 10⁹/L; ANC ≥ 1.0 x 10⁹/L without the use of hematopoietic growth factors
9. Coagulation tests within the normal range
10. Bilirubin and creatinine less than 2 times the upper limit of normal for the institution
11. AST and ALT less than 3 times the upper limit of normal for the institution
12. Potassium, magnesium and phosphorus within the normal range for the institution (supplementation is permissible)
13. Willing to use accepted and effective methods of contraception during the study (both men and women as appropriate) and for 3 months after the last dose of SNDX-275
14. Patient or legally acceptable representative has granted written informed consent before any study-specific procedure (including special screening tests) is performed

EXCLUSION:

1. Prior stem cell transplant
2. Symptomatic CNS involvement
3. Prior treatment with an HDAC inhibitor
4. Concurrent anticancer therapy, with the exception of radiotherapy for a non-target study lesion
5. Currently taking medication(s) on the prohibited medication list
6. Systemic chemotherapy or treatment with an investigational agent within 28 days before enrollment
7. Current use of valproic acid
8. Untreated or unstable brain metastases, or taken steroids for this condition within 4 weeks of study drug administration
9. Currently active second malignancy, or any malignancy within the last 5 years other than cured basal or squamous cell skin carcinoma, cervical carcinoma in situ, or superficial bladder cancer
10. Inability to swallow oral medications or a gastrointestinal malabsorption condition
11. Uncontrolled infection requiring IV antibiotics, antivirals, or antifungals, known HIV infection, or active hepatitis B or C infection
12. Abnormal cardiac function as defined as clinically significant findings on ECG (multifocal PVCs, ST-T wave changes consistent with myocardial infarction or acute ischemia, QTc greater than 500 milliseconds), tachycardia, or left ventricular ejection fraction less than 40% on MUGA scan
13. Another serious or uncontrolled medical condition within 3 months of enrollment such as hypertension, diabetes mellitus, or suppressed immune system
14. Known hypersensitivity to benzamides
15. Morbid obesity
16. Women who are currently pregnant or breast-feeding
17. Patient is currently enrolled in (or completed within 28 days) another investigational drug study
18. Patient unavailable for on-study or follow-up assessments
19. Patient has any kind of medical, psychiatric, or behavioral disorder that places the patient at increased risk for study participation or compromises the ability of the patient to give written informed consent and/or to comply with study procedures and requirements