RecruitingPhase 1Biological interventionPrototype DAA/TAA Vaccine Targeting MUC1 for Immune Interception and Prevention in Ductal Carcinoma In SituWomen with biopsy-proven ductal carcinoma in situ (DCIS) will be enrolled into two cohorts. One cohort will receive neoadjuvant therapy with an aromatase inhibitor or selective estrogen receptor modulator (SERM) for about 12 weeks prior to surgery at 12 weeks. The second cohort will receive neoadjuvant therapy with an aromatase inhibitor or selective estrogen receptor modulator and MUC1 vaccination (MUC1 peptide + Hiltonol®) pre-operatively at baseline, and weeks 2 and 10, followed by surgery at about 12 weeks. Patients in the vaccine cohort will be offered an optional boost vaccine 6 months after surgery.