Background: The pathophysiology of capecitabine induced hand-foot syndrome (HFS) includes activation of cyclooxygenase (COX)-2, leading to an upregulation of the inflammatory cascade. Prophylaxis with oral celecoxib was previously reported to be associated with a significantly lower frequency of HFS (grade 1 [29.0% vs. 72.0%, p < 0.001] and grade 2 [11.8% vs. 30.0%, p=0.024]) (1). The findings were confirmed in a phase III trial (2). However, the associated systemic adverse events limit routine prophylactic use. Till date, no clinical trials have assessed the role of topical non-steroidal anti-inflammatory drugs (NSAIDs) in preventing HFS. Methods: In this investigator-initiated randomised phase III double-blind, placebo controlled, parallel group trial, a total of 264 patients with any stage breast or gastrointestinal cancer planned to receive capecitabine as a single agent or in combination with other chemotherapy will be randomised (1:1) to 1% topical diclofenac or placebo (base for 1% topical diclofenac) arm at a single tertiary care cancer centre in India. Randomization will be done by stratified (male vs female, and capecitabine mono therapy vs combination) permuted block method using a computer generated random sequence and allocation concealment will be done by using sealed opaque envelopes. In both the arms, patients will be asked to apply 1 fingertip unit (FTU) of topical medication on both surfaces of bilateral hands twice daily for a total duration of 12 weeks or till development of grade 2 or higher HFS, whichever is earlier. The primary objective is to compare the effect of topical diclofenac with placebo in preventing clinically significant HFS (incidence of the National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 grade 2 or higher HFS). The secondary objectives include comparison of topical diclofenac with placebo on (i) incidence of NCI CTCv5.0 all grade HFS, (ii) time to develop grade ≥2 HFS from start of capecitabine, (iii) patient-reported outcomes using HFS-14 questionnaire (iv) adherence with topical application using self-reported adherence diary, (v) capecitabine dose reductions, delays and cessation due to HFS and (vi) safety profile (NCICTCv5.0). The tertiary correlative endpoint is to correlate the occurrence and severity of HFS with serum COX-2 levels and polymorphism of dihydropyrimidine dehydrogenase (DPPD) enzyme. The trial is registered at the Clinical Trial Registry of India (CTRI/2021/01/030592). Till date, we have enrolled 12/264 patients. (1) Zhang RX et al. J Cancer Res Clin Oncol. 2011;137(6):953-957. (2) Zhang RX et al. Annals of oncology. 2012;23(5):1348-1353. Clinical trial information: CTRI/2021/01/030592.