PI is leaving institution and this protocol will not be further pursued at this institution.

Radiotherapy is a mainstay of treatment in breast cancer treatment, in the adjuvant setting. Radiation dermatitis occurs in up to 65% of these patients; currently, there is no standard of care for this treatment-related toxicity. The aim of this study is to investigate the safety and tolerability (Phase I) and preliminary efficacy (Phase II) of prophylactic esomeprazole cream (termed "Dermaprazole") in patients who require radiation for breast cancer in the adjuvant setting.

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.

Inclusion Criteria:

1. Women with breast cancer, treated with ipsilateral i) Simple (total) mastectomy, OR ii) Modified radical mastectomy, OR iii)Radical mastectomy, OR iv) Segmental mastectomy, OR v) Skin sparing/nipple sparing mastectomy
2. Histological diagnosis of invasive ductal or lobular carcinoma (diagnosed within 2 years of enrollment)
3. Planned to receive adjuvant chest wall radiation of at least 40Gy or higher biologically equivalent dose (BED)
4. Age 18 years or older
5. Women of childbearing potential (any woman with menses in the last 12 months) must agree to pregnancy testing and contraceptive use throughout the study period. Testing consists of human chorionic gonadotropin (HCG) urine testing, which if suspected to be falsely positive may be confirmed by ultrasound. If ultrasound is negative, patient is considered not pregnant and eligible for inclusion in the study. In addition to routine contraception method such as barrier devices, hormonal methods, and intrauterine devices, heterosexual celibacy, and surgical sterility (hysterectomy, bilateral oophorectomy, bilateral tubal ligation, or a partner with history of vasectomy) is considered acceptable. If a celibate patient chooses to become sexually active during the study period, she must use one of the listed methods of contraception throughout the study period.
6. Eastern Cooperative Oncology Group (ECOG) performance status 0 to 2
7. Written Informed Consent
8. History and Physical within 12 weeks of enrollment

Exclusion Criteria:

1. Prior chest wall radiotherapy
2. Any serious medical condition or illness that would preclude the safe administration of the study drug including, but not limited to: active infection, symptomatic heart failure, unstable angina, psychiatric illness or social situations that would limit compliance with treatment
3. Concurrent chemotherapy
4. Biopsy-proven epidermal involvement or positive margins
5. Open wound at time of consultation, or delayed surgical wound healing as defined as open wound >8 weeks post-op
6. Known active collagen vascular disease such as systemic lupus erythematous, scleroderma or dermatomyositis.
7. Allergy or sensitivity to proton pump inhibitors
8. Pregnancy or breast feeding
9. Use of clopidrogrel, St. Johns Wort, rifampin, or methotrexate

The AE collection/reporting period will begin with the first day of application of Dermaprazole and will end 30 days after radiation, up to 6 months.