This study tests if diclofenac, a common pain reliever, can help treat patients with non-small cell lung cancer (NSCLC) that has spread (metastatic) while they are on immunotherapy. Immunotherapy uses the body's immune system to fight cancer, using medications like pembrolizumab and nivolumab. Diclofenac, a non-steroidal anti-inflammatory drug (NSAID), may reduce inflammation and improve the effectiveness of immunotherapy. The study will check if diclofenac can help stop the cancer from growing or spreading.

Key Points:

• Participants take diclofenac twice daily and receive regular immunotherapy every 3-4 weeks.
• The study includes blood tests and scans like CT, PET, or MRI to monitor progress.
• After treatment, participants are followed up every 12 weeks for up to a year.

To join, participants must be 18 or older, have advanced NSCLC, and have been on immunotherapy for at least 12 weeks. They also need to meet specific health criteria. People on certain blood thinners or with some health conditions might not qualify. Safety and effectiveness will be monitored throughout the study.