Lung cancer is the leading cause of cancer-related deaths worldwide. Most patients present with advanced inoperable disease. Traditionally, responses to treatments are evaluated using different imaging modalities, which can sometimes be confusing. This is particularly more relevant in stage 3 disease where, after radiation therapy, persistent tumors on scans can represent active disease or scar tissue. We have been evaluating role of circulating tumor cells (CTCs) in that setting. Here we present the case of a 68-year-old male with stage 3 disease whose primary tumor responded to chemoradiotherapy on imaging, but whose CTC count was higher than the pre-treatment value. The patient later developed liver metastases. In this case, the CTC count more accurately predicted the patient's prognosis and highlights the need for exploration of the CTC count as a tool supplemental to imaging modalities.