Solid tumors have the tendency to spread to other organs in around 26% of cases, with many cases involving the bone causing severe bone destruction and pain that reduces patients' quality of life. Palliative radiation therapy is used as a standard of care to decrease cancer-related bone pain, as it has been proven to provide pain relief in many patients, either partially or totally, within only a few weeks. However, some patients experience worsening of bone pain especially within the first 10 days after radiation therapy, this is called bone pain flare, and its incidence is estimated to be around 40%. This pain flare tends to further reduce these patients' quality of life considering their main illness, which necessitates its prevention or alleviation.

Non-Steroidal Anti-inflammatory Drugs (NSAIDs) which are a key component of the World Health Organization (WHO) analgesic options used to alleviate cancer pain have not had a good share of published trials in the prevention of bone pain flares.

In this light the investigators aim to conduct a double-blinded, placebo-controlled randomized controlled trial to investigate the effectiveness of NSAIDs, specifically Proxen, in preventing bone pain flares after palliative radiotherapy, and as a secondary endpoint they will compare the quality of life and side effects experienced by patients in either group.

Inclusion Criteria:

• Age 18 years or older
• Primary Solid tumor (Any type of solid tumor)
• Painful bone metastases which are otherwise uncomplicated (no fracture and no neurologic symptoms due to nerve impingement or compression)
• Baseline pain score on a numeric rating scale (0-10) of at least 2
• Stable dose and schedule of narcotic medications prescribed

Exclusion Criteria:

• Hematologic malignancy
• Previously irradiated bone
• Current use of steroids
• Current use of NSAIDs which cannot be stopped before randomization
• Contraindications for NSAIDs (hypersensitivity, PUD, prior GI bleed, CKD, HTN, HF, AERD/asthma)
• Contraindications for PPIs