Topical Dermaprazole for Radiation Dermatitis in Breast Cancer Patients (TOPAZ)

All study participants will begin using Dermaprazole for 1-2 weeks prior to receiving radiation. During the CT Simulation, study participants will be instructed to apply Dermaprazole in a "patch test" area - an area of the chest outside of the field of radiation. This is to assess for immediate skin reactions including itching, irritation and allergy. If there are no immediate allergic reactions at the conclusion of the simulation visit, the study participant will be instructed to apply the cream in the patch test for 2-4 days to assess for contact dermatitis and if no itching or rash at that time (evaluation will be conducted via phone call). Patients will be questioned regarding any visible skin changes or irritation (itching, peeling, scaling), and patients responding in the affirmative will be asked to present for clinic visit or send photographs for visual classification according to the scale outlines in Table 1 below. Skin reactions matching a score of 3 will be evaluated with a second clinic visit between 2 to 7 days after initial application. Any skin reactions of score 4 or 5 at final assessment will be deemed to be positive for allergic contact dermatitis, and patients will be deemed positive for allergic contact dermatitis. Two dose levels of Dermaprazole (1% and 2%) will be evaluated in the combination Phase I/II dose escalation/de-escalation BOIN design study evaluating preliminary efficacy at the Maximum Feasible Dose (MFD). The Dermaprazole will be initiated at a dose of 1% and escalated to 2% as appropriate based on the number of adverse events. A Dose Limiting Toxicity (DLT) will be defined as any of the following: a) any \> Grade 2 skin toxicity outside the radiation field (Macules/ papules covering 10-30% of the area with or without symptoms of pruritus, burning, tightness), b) any \> Grade 2 radiation dermatitis (Moderate to brisk erythema; patchy moist desquamation, within the radiation field that is probably or definitely related to Dermaprazole. Dermatitis will be evaluated by a radiation oncologist on a weekly basis using the Common Terminology Criteria for Adverse Events (CTCAE) V5.0 criteria. Patient reported quality of life will be evaluated using a validated survey instrument called SkinDex16.