Pancoast tumors are non-small cell lung tumors, which can invade the ribs, vertebrae, sympathetic ganglia and brachial plexus. In this study, a patient with right-sided Pancoast tumor presented with intractable chronic pain on the right neck, upper extremity and chest wall. The chronic pain associated with Pancoast tumor, which was difficult to treat with opioids and other medications, was effectively treated with a high-thoracic erector spinae plane block (ESPB). Prolonged analgesia was provided with an ESP catheter to wean the patient from opioids. This case report provides an example where the novel interfacial ESP block can provide pain relief in challenging situations such as lung malignancies involving deeper structures and extensive areas of pain.