Inclusion Criteria:

- Histologically confirmed endometrial carcinoma

- Recurrent or persistent disease

- Histologic confirmation of the original primary tumor is required

- Refractory to curative therapy or standard treatments

- Measurable disease

- At least 1 unidimensionally measurable lesion ≥ 20 mm by conventional
techniques, including palpation, plain x-ray, CT scan, or MRI OR ≥ 10 mm by
spiral CT scan

- Must have at least 1 target lesion

- Tumors within a previously irradiated field are considered non-target
lesions

- Disease in an irradiated field as the only site of measurable disease
is considered a target lesion provided there has been clear
progression of the lesion since the completion of prior radiotherapy

- Must have received 1 prior chemotherapy regimen for endometrial carcinoma

- Initial therapy may have included high-dose therapy, consolidation, or extended
therapy administered after surgical or non-surgical assessment

- No more than 1 additional prior cytotoxic regimen for recurrent or persistent
disease

- Tumor accessible to guided core needle or fine needle biopsy

- Ineligible for a higher priority GOG protocol (e.g., any active GOG phase III
protocol for the same patient population)

- Performance status - GOG 0-2 (for patients who have received 1 prior treatment
regimen)

- Performance status - GOG 0-1 (for patients who have received 2 prior treatment
regimens)

- Absolute neutrophil count ≥ 1,500/mm^3

- Platelet count ≥ 100,000/mm^3

- Bilirubin ≤ 1.5 times upper limit of normal (ULN)

- SGOT ≤ 2.5 times ULN

- Alkaline phosphatase ≤ 2.5 times ULN

- Creatinine ≤ 1.5 times ULN

- Cardiac ejection fraction normal by echocardiogram or MUGA

- No gastrointestinal (GI) tract disease resulting in an inability to take oral
medication

- No malabsorption syndrome

- No requirement for IV alimentation

- No uncontrolled inflammatory GI disease (e.g., Crohn's or ulcerative colitis)

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

- No active infection requiring antibiotics

- No sensory or motor neuropathy > grade 1

- No history of allergic reaction attributed to compounds of similar chemical or
biological composition to lapatinib

- No other invasive malignancy within the past 5 years except nonmelanoma skin cancer

- At least 4 weeks since prior immunologic agents for the malignant tumor

- No prior trastuzumab (Herceptin^®) or any target-specific therapy directed to the HER
family (e.g., gefitinib, erlotinib, or cetuximab)

- At least 6 weeks since prior nitrosoureas or mitomycin for the malignant tumor and
recovered

- No prior non-cytotoxic chemotherapy for recurrent or persistent disease

- At least 1 week since prior hormonal therapy for the malignant tumor

- Concurrent hormone replacement therapy allowed

- Recovered from prior radiotherapy

- Recovered from prior surgery

- No prior surgery affecting absorption

- At least 4 weeks since other prior therapy for the malignant tumor

- No prior lapatinib

- No prior anticancer treatment that would preclude study treatment

- Concurrent oral anticoagulants (e.g., warfarin) allowed provided there is increased
monitoring of INR

- No concurrent CYP3A4 inducers or inhibitors

- No concurrent combination antiretroviral therapy for HIV-positive patients