Repeated treatments with TGF-β3 mouthwash before and during chemotherapy did not influence the onset, duration, or severity of oral mucositis in 116 patients with breast cancers, lymphomas, and other solid cancers. There were no clinical differences between treatment and placebo regarding safety, and no evidence of systemic absorption of TGF-β3. The gene discussed is TGFB3; the disease is mucositis.