Oral Mucositis Not Reduced with Dexamethasone Mouthwash in Early Breast Cancer

The use of dexamethasone mouthwash did not significantly reduce all-grade oral mucositis for patients with early breast cancer, according to results from the multicenter, randomized phase 3 SMASH-BC trial (jRCTs071240036) presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting.

In the intervention group, which received steroid mouth wash, 58.8% of patients experienced oral mucositis compared with 63.2% in the control group, which recieved a tap water rinse (RR, 0.93; 95% CI, 0.75-1.15), with a risk difference of –4.4 (95% CI, –17.3 to 8.4; P = .59). Moderate or high oral mucositis by patient reported outcomes (PRO) CTCA was reported by 13.2% of the intervention group vs 18.9% of the control group (RR, 0.70; 95% CI, 0.38-1.29), with a risk difference of –5.7 (95% CI, –15.4 to 4.0; P = .33).

“In conclusion, steroid mouthwash did not significantly reduce oral mucositis in this study, and routine prophylactic use is not recommended,” Sayaka Kuba, PhD, deputy director, Center for Comprehensive Community Care Education, Nagasaki University Graduate School of Biomedical Sciences, said during the presentation.

A total of 230 patients were randomly assigned 1:1 to receive chemotherapy with steroid mouthwash of a 0.01% elixir (n = 117) or chemotherapy with a tap water rinse (n = 113). In each respective group, a total of 113 and 106 patients received their intervention. In the steroid mouthwash group, 3 patients withdrew consent and 1 did not receive the intervention; in the control group, 6 patients withdrew consent and 1 did not receive chemotherapy. Notably, the study was powered to identify a reduction from 55% to 35% with a 2-sided α = .05.

The primary end point was incidence of all-grade oral mucositis at 8 weeks which, was assessed by electronic PROs. Secondary end points were grade 2 or higher oral mucositis, duration of oral mucositis, quality of life, and adherence.

Patients were enrolled if they had early breast cancer with planned chemotherapy. Chemotherapy included standard or dose-dense doxorubicin/epirubicin plus cyclophosphamide (AC/EC), taxotere/cyclophosphamide, and AC/EC plus pembrolizumab (Keytruda). Patients were stratified by regimen, institution, or smoking status.

The median patient age was 54 years in the intervention group vs 53 in the control group; 100% vs 99% were female, 96% vs 95% had an ECOG performance status of 0, 57% vs 52% were postmenopausal, 65% vs 62% were preoperative at the time of chemotherapy, 87% vs 88% received AC/EC, and 12% vs 11% smoked.

Any grade symptoms in the intervention and control arms included dry mouth (87% vs 87%), difficulty swallowing (66% vs 49%), mouth/throat sores (65% vs 76%), taste changes (89% vs 85%), and oral candidiasis (5% vs 0%). Moderate or higher AEs included nausea (63% vs 59%), constipation (63% vs 58%), taste changes (63% vs 43%), decreased appetite (54% vs 56%), and oral candidiasis (5% vs 0%).

“Safety profiles were generally comparable between groups. However, oral candidiasis was more frequent in the intervention group. Compared with our phase 2 study, this may be related to limited dental care,” Kuba noted. “In the phase 2 study, regular dental visits were mandatory whereas approximately 70% of patients in the current study had no dental visits. Future studies should focus on identifying high-risk patients and biomarker strategies.”

Disclosures: Kuba reported receiving honoraria from Chugai/Roche, Daiichi Sankyo/UCB Japan, Exact Sciences, and Gilead Sciences; research funding from Pfizer/Seagen; and expert testimony from Pfizer.

Reference

Kuba S, Hagiwara Y, Shibata N, et al. A randomized phase III trial of dexamethasone mouthwash to prevent chemotherapy-induced oral mucositis in patients with breast cancer. J Clin Oncol. 2026;44(suppl 16):12017. doi:10.1200/JCO.2026.44.16_suppl.12017