Inclusion Criteria:

- Histologically confirmed prostate cancer

- Biochemical disease progression after prior definitive surgery or radiotherapy, as
evidenced by all of the following:

- Three consecutive rising prostate-specific antigen (PSA) levels obtained ≥ 6
weeks apart within the past 6 months

- Most recent PSA > 0.4 ng/mL after prostatectomy (1.5 ng/mL after radiotherapy)

- PSA doubling time < 1 year

- Hormone-sensitive disease, as evidenced by total testosterone > 150 ng/dL within the
past 4 weeks

- WBC ≥ 3,000/mm^3

- Granulocyte count ≥ 1,500/mm^3

- Platelet count ≥ 100,000/mm^3

- Bilirubin normal

- Alkaline phosphatase normal

- AST and ALT ≤ 2.5 times upper limit of normal

- PT/INR normal

- Creatinine normal or Creatinine clearance ≥ 60 mL/min

- Cardiac ejection fraction normal by echocardiogram or MUGA within the past 4 weeks

- Prior radiotherapy, surgery or local ablative procedures as curative salvage therapy
allowed

- At least 1 year since prior neoadjuvant or adjuvant chemotherapy or hormonal therapy

- At least 1 year since prior therapy that modulates testosterone levels (e.g.,
luteinizing hormone-releasing hormone agonists/antagonists or antiandrogens)

- At least 1 year since prior investigational agents

- More than 6 months since prior 5α-reductase inhibitors, megestrol, systemic steroids,
ketoconazole or herbal supplements

- At least 7 days to 6 months since prior CYP3A4 inducers or inhibitors as determined
by the treating physician

- Age 18 and over

- ECOG Performance status 0-1

- Able to swallow and retain oral medication

- Fertile patients must use effective contraception

Exclusion Criteria:

- Metastatic disease

- Other malignancy within the past 5 years except curatively treated nonmelanoma skin
cancer

- Unstable arrhythmias on ECG

- Rate-controlled asymptomatic atrial fibrillation allowed

- Symptomatic congestive heart failure

- Unstable angina pectoris

- GI tract disease resulting in either of the following:

- Malabsorption syndrome

- Requirement for IV alimentation

- Uncontrolled inflammatory GI disease (e.g., Crohn's disease or ulcerative colitis)

- Ongoing or active infection

- Psychiatric illness or social situation that would preclude study compliance

- History of allergic reaction attributed to compounds of similar chemical or biologic
composition to lapatinib

- Other uncontrolled illness

- Prior vaccine therapy or immunotherapy for prostate cancer

- Prior surgery affecting gastrointestinal (GI) tract absorption

- Concurrent ketoconazole

- Concurrent CYP3A4 inducers or inhibitors

- Concurrent antacids within 1 hour before or after study drug administration

- Other concurrent investigational agents or anticancer therapy

- Concurrent antiretroviral therapy for HIV-positive patients