Background: Our previous studies showed that vasoconstrictor applied topically to rat skin minutes before irradiation completely prevented radiodermatitis. Here we report on a Phase IIa study of topically applied NG12-1 vasoconstrictor to prevent radiodermatitis in post-lumpectomy breast cancer patients who received at least 40 Gray to the whole breast using standard regimens.Methods: Patients had undergone surgery for Stage Ia, Ib, or IIa infiltrating ductal or lobular carcinoma of the breast or ductal carcinoma in situ. NG12-1 formulation was applied topically to the same 50-cm2 treatment site within the radiation field 20 min before each daily radiotherapy fraction.Results: Scores indicated significant reductions in radiodermatitis at the NG12-1 treatment site versus control areas in the same radiotherapy field. The mean dermatitis score for all subjects was 0.47 (SD 0.24) in the NG12-1-treated area versus 0.72 (SD 0.22) in the control area (P = 0.022). Analysis by two independent investigators indicated radiodermatitis reductions in 9 of the 9 patients with scorable radiodermatitis severity, and one patient with insufficient radiodermatitis to enable scoring. There were no serious adverse events from NG12-1 treatment.Conclusions: Thirty, daily, NG12-1 treatments, topically applied minutes before radiotherapy, were well tolerated and conferred statistically significant reductions in radiodermatitis severity (P = 0.022).Trial Registration: NCT01263366 ; clinicaltrials.gov. [ABSTRACT FROM AUTHOR]