Cerebrospinal Fluid Levels of Erlotinib in Patients Receiving Erlotinib For Stage III Non-Small Cell Lung Cancer

DISEASE CHARACTERISTICS: * Patients must be enrolled in the trial: "A Phase I/II Trial of Neoadjuvant Paclitaxel, Carboplatin and OSI-774 (Tarceva) with Concurrent Accelerated Hyperfractionation Radiation Followed by Maintenance Therapy with OSI-774 for Stage III Non-Small Cell Lung Cancer," Principal Investigator: T. Mekhail, M.D. * Patient must be in maintenance therapy phase of the study and have received erlotinib for ≥ 1 week * No known CNS primary or metastatic cancer at any time prior to time of enrollment * No MRI evidence of pathological enhancement at the time of study entry PATIENT CHARACTERISTICS: * Patients must use adequate birth control measures while in the study * No significant side effects to erlotinib that require dose reduction or interruption * None of the following medical issues which could make a lumbar puncture unsafe: * Platelets \< 100,000/mm³ * INR \> 1.1 * Known bleeding dyscrasia * Absolute neutrophil count \< 1,500/mm³ * Ongoing systemic bacterial infection PRIOR CONCURRENT THERAPY: * Patients on modest or anti-epileptic therapy must be on nonenzyme-inducing drug only, including any of the following: * Neurontin * Lamictal * Depakote, Depakene * Felbatol * Keppra * Gabitril * Topimax * Zonegran * No concurrent enzyme-inducing anti-epileptic drugs such as phenytoin, carbamazepine, or phenobarbital * No concurrent other drug known to affect the metabolism of erlotinib * No concurrent anticoagulant therapy