Lapatinib in Metastatic Breast Cancer Resistant to Hormone Therapy

Inclusion Criteria: Patients with histologically or cytologically proven metastatic breast cancer. Patients with either estrogen or progesterone receptor positivity on the most recently examined tumor biopsy. Patients must have most recently been using an anti-estrogen (tamoxifen, toremifene, raloxifene, or fulvestrant) or an aromatase inhibitor. Patients must have had either a partial response or better, or stable disease for 24 weeks or longer, followed by disease progression, on the current or most recent hormonal therapy for management of metastatic breast cancer. Patients must be enrolled within six weeks of defining disease progression on hormonal therapy. Patients must have stopped fulvestrant at least four weeks prior and other endocrine therapy at least two weeks prior to enrollment on study. Patients must have either measurable disease or at least one evaluable bone lesion that has not been irradiated. Measurable disease is not necessary. Estimated life expectancy of at least 6 months. ECOG performance status 0-2. Adequate hematologic, hepatic, and renal function. Patients must be post-menopausal, or they must be practicing either abstinence or an adequate method of contraception, or their sexual partner must be sterile. All patients must be able to swallow, retain, and absorb oral medications. All patients must be able to give informed consent indicating that they are aware of the investigational nature of this study. Exclusion Criteria: Patients may not have received an investigational agent within the prior four weeks. Patients may not have received trastuzumab within three weeks of study entry. Patients may not have had major surgery within the prior two weeks. Patients may not have Class III or IV heart failure as defined by the NYHA functional classification system. Patients may not have a left ventricular ejection fraction < 40% based on MUGA or echocardiogram. Patients may not have uncontrolled brain metastases or leptomeningeal disease. Patients may not have rapidly progressive visceral metastases. Patients may not have a serious illness or conditions including clinically significant cardiac disease, angina pectoris, serious psychiatric disorder, or an active infection. Patients may not be receiving concurrent medications (listed in the protocol) which may interact with lapatinib during treatment with lapatinib.