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A 64-year-old Asian woman diagnosed with synchronous breast ductal carcinoma in situ (DCIS) and stage IV EGFR-mutated non-small cell carcinoma of the lung (NSCLC). A decision was made to defer management of the DCIS and initiate Osimertinib for lung cancer treatment, since this was a life-limiting diagnosis. At 9 months, restaging FDG-PET CT showed an interval response in the NSCLC and complete loss of FDG avidity at the biopsy-proven DCIS site. Breast MRI confirmed complete imaging resolution of the DCIS. The clinical resolution of breast DCIS during third-generation EGFR inhibitor therapy has not been previously reported in humans and highlights a potential role for the EGFR/HER2 (ERBB) pathway in pre-invasive breast cancer.