Inclusion Criteria:

- Women must not be pregnant or breastfeeding

- All females of childbearing potential must have a blood test within 2 weeks prior to
registration to rule out pregnancy

- A female of childbearing potential is any woman, regardless of sexual
orientation or whether they have undergone tubal ligation, who meets the
following criteria: 1) has not undergone a hysterectomy or bilateral
oophorectomy; or 2) has not been naturally postmenopausal for at least 24
consecutive months (i.e., has had menses at any time in the preceding 24
consecutive months)

- Women of childbearing potential and sexually active males must be strongly advised to
use an accepted and effective method of contraception

- Patients must have histologically or cytologically confirmed:

- Extensive stage small cell lung cancer (SCLC) (Phase I and II)

- The extensive disease SCLC classification for this protocol includes all
patients with disease sites not defined as limited stage

- Limited-stage disease category includes patients with disease
restricted to one hemithorax with regional lymph node metastases,
including hilar, ipsilateral and contralateral mediastinal, and/or
ipsilateral supraclavicular nodes

- Extensive-disease patients are defined as those patients with
extrathoracic metastatic disease, malignant pleural effusion, or
bilateral or contralateral supraclavicular adenopathy

- Stage IV (M1a or M1b according to American Joint Committee on Cancer [AJCC]
Staging Manual, 7th edition) large cell neuroendocrine non-small cell lung
cancer (NSCLC) (Phase I only)

- Small cell carcinoma of unknown primary or extrapulmonary origin and must be a
candidate for systemic therapy (phase I only)

- Patients must have measurable or non-measurable disease based on Response Evaluation
Criteria in Solid Tumors(RECIST) 1.1; baseline measurements and evaluations of all
sites of disease must be obtained =< 4 weeks prior to registration (phase I)

- Patients must have measurable disease based on RECIST 1.1; baseline measurements and
evaluations of all sites of disease must be obtained =< 4 weeks prior to registration
(phase II)

- Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1

- Absolute neutrophil count >= 1,500/mm^3

- Platelets >= 100,000/mm^3

- Leukocytes >= 3,000/mm^3

- Hemoglobin >= 9 g/dL

- Total bilirubin =< 1.5 times institutional upper limit of normal (ULN)

- Aspartate aminotransferase (AST) (serum glutamic oxaloacetic transaminase [SGOT]) and
alanine aminotransferase (ALT) (serum glutamic pyruvate transaminase[SGPT]) =< 3
times institutional ULN (=< 5 times if liver function test [LFT] elevations due to
known liver metastases)

- Creatinine =< 1.5 X ULN OR creatinine clearance >= 60 mL/min/1.73 m^2 for patients
with creatinine levels > 1.5 x ULN

- Patients with central nervous system (CNS) metastases or a history of CNS metastases
are ineligible

- Patients cannot have had prior chemotherapy or biologic therapy for SCLC (phase I and
II) or large cell neuroendocrine NSCLC (phase I only), or small cell carcinoma of
unknown primary or extrapulmonary origin (phase I only)

- Patients receiving prior radiation cannot register within 7 days after completion of
radiation, and must have resolved adverse events attributed to radiation to =< grade
1; no previous irradiation to the only site of measurable or evaluable disease,
unless that site had subsequent evidence of progression

- Patients may not be receiving any other investigational agents while on study

- Patients must NOT have active seizure(s) or history of seizure(s)

- Patients must NOT have history of allergic reactions attributed to compounds of
similar chemical or biologic composition to veliparib or other agents used in the
study

- Patients must NOT have uncontrolled intercurrent illness including, but not limited
to, ongoing or active infection, symptomatic congestive heart failure, unstable
angina pectoris, uncontrolled cardiac arrhythmia, or psychiatric illness/social
situations that would limit compliance with study requirements

- Human immunodeficiency virus (HIV)-positive patients on combination antiretroviral
therapy are ineligible

- Patient must be able to swallow pills