 We will review medical records to identify patients who underwent percutaneous needle biopsy of a lung mass between 5101 and 103004. If the pathology report indicates that the biopsy showed no evidence of malignancy, we will examine the medical record for a gold standard diagnosis of the lesion in question, including the pathology result from a surgical resection or a repeat biopsy, imaging follow-up demonstrating regression of the lesion or size stability for at least 2 years, or clinical follow-up for at least 2 years with no clinical evidence of malignant disease. If this information is not available in the University Hospital medical record, we will contact the patient to obtain consent for follow-up using external sources physician records, imaging studies, pathology reports. 