Topical Diclofenac for Hand-Foot Syndrome Prevention in Colorectal and Gastric Cancer on Capecitabine (DICLO-HFS)

Hand-foot syndrome (HFS), also known as palmar-plantar erythrodysesthesia, is a common dermatologic toxicity of fluoropyrimidine chemotherapy such as capecitabine. Clinically significant HFS (grade ≥2) can negatively impact treatment adherence and quality of life by necessitating dose interruptions or reductions. The underlying mechanisms are not fully understood, but inflammatory pathways, including cyclooxygenase-2 (COX-2) signaling, are thought to contribute. Preventive strategies for HFS remain limited. Celecoxib, a systemic COX-2 inhibitor, has been shown to reduce HFS incidence but is not widely adopted due to safety concerns. Topical diclofenac gel, a locally acting nonsteroidal anti-inflammatory drug (NSAID), represents a potential low-toxicity prophylactic approach. This prospective, multicenter observational study is designed to evaluate the prophylactic effect of topical diclofenac in patients with colorectal or gastric cancer initiating capecitabine therapy. The study is conducted at Gazi University Faculty of Medicine and Ankara Etlik City Hospital. Eligible participants are adults scheduled to receive capecitabine-based therapy who have not received prior chemotherapy. Participants are managed according to physician preference: Topical diclofenac group: Patients apply 1% topical diclofenac gel to clean, dry skin on the hands and feet twice daily during capecitabine treatment. Observation group: Patients are followed with active monitoring without prophylactic intervention. The primary endpoint is the incidence of grade 2 or 3 HFS, assessed weekly using the Common Terminology Criteria for Adverse Events (CTCAE). Secondary endpoints include time to onset of HFS and the proportion of patients requiring capecitabine dose reductions due to HFS. The planned enrollment is approximately 150 patients, with follow-up continuing until either the onset of clinically significant HFS or completion of capecitabine therapy.