Ten (10) patients will be randomized before the first radiation treatment to receive ST266 (4ml) and saline placebo (4ml), one to the medial segment and the other to the lateral segment. The area of the breast will be divided into two, roughly equal parts, medial and lateral. The randomization scheme will be equal in each of two cohorts. The first cohort will receive ST266 and saline placebo applied to intact skin beginning immediately following the first radiation treatment, to continue immediately following each of ten (10) consecutive radiation treatments.

Ten (10) patients will be randomized before the first radiation treatment to receive ST266 (4ml) and saline placebo (4ml), one to the medial segment and the other to the lateral segment. The area of the breast will be divided into two, roughly equal parts, medial and lateral. The randomization scheme will be equal in each of two cohorts. The second cohort will receive ST266 and saline placebo applied to inflamed skin (after inflammation is first noted) beginning immediately following the radiation treatment, to continue immediately following each of ten (10) consecutive radiation treatments.

Patients will receive ST266 spray, to half the breast and saline to the other half (blinded) after each of ten consecutive radiation therapy treatments. ST266 and saline will be sprayed onto the breast to deliver 0.01 ml/cm2.

Quality of Life (QOL) will be evaluated using a QOL Assessment (general to breast cancer patients receiving radiation therapy following tumor removal) and a QOL Supplement (specific to subjects receiving trial treatment). Both documents include subsets of questions, each with a different subscale. The assessments include both lifestyle QOL factors (sleep, activity, friends/family, general life enjoyment, etc.) and breast condition (pain, appearance, ect.). This secondary endpoint will focus on the QOL Supplement, comparing breast condition by treatment, noting changes in both the medial and lateral aspects breast including breast texture (thickening and hardness), pain, tenderness, shape, sensitivity, swelling, redness, itching, flaking skin, blistering and fluid leak. The patient will note, for each item, in which side of the breast they are experiencing the negative breast condition or if there is no difference.

Cosmesis will be evaluated by photography and investigator assessment using the cosmesis form in National Surgical Adjuvant Breast and Bowel Project (NSABP) Protocol B-39, A Randomized Phase III Study of Conventional Whole Breast Irradiation Versus Partial Breast Irradiation for Women with Stage 0, I, or II Breast Cancer. The following factors will be evaluated in the skin: telangiectasia, atrophy, scarring, pigmentation, erythema, fat necrosis, and fibrosis.