Past medical history was notable for recurrent urinary tract infections, for which the patient had been taking nitrofurantoin prophylaxis for 6 months at a dose of 100 mg per day. Laboratory evaluation revealed markedly elevated aminotransferases, with AST of 268 and ALT of 419, despite the absence of metastatic involvement of the liver on the staging investigations. Bilirubin was normal. Because of concerns about possible combined pulmonary and hepatic nitrofurantoin toxicity, it was recommended that the patient stop taking the prophylactic nitrofurantoin. A second biopsy of the RLL lung mass was performed to obtain additional tissue for molecular analysis. This biopsy again showed adenocarcinoma. The patient's tumor was wild type for epidermal growth factor receptor, anaplastic lymphoma kinase, and KRAS.