This is a multicenter, open-label, 2-arm study comparing erlotinib exposure in cancer patients with adequate hepatic function versus cancer patients with moderate hepatic impairment. All patients will receive a single 150 mg dose of erlotinib on Day 1 followed by 96 hours of plasma sampling for PK and protein binding studies. Patients may then enter the maintenance phase of the study and continue to receive erlotinib until disease progression or unacceptable toxicity.