What happened, in summary

A 59-year-old woman undergoing routine breast screening was found to have a broad area of calcifications in the left breast. Biopsy showed low-to-intermediate grade ductal carcinoma in situ, or DCIS. At the same time, imaging showed abnormal lymph nodes, raising concern because DCIS alone would not usually explain nodal spread.

Several months earlier, she had developed left supraclavicular swelling shortly after receiving a COVID-19 vaccine in the same arm. Biopsy of an abnormal axillary node showed reactive lymphoid tissue rather than cancer, and the clinical team concluded that the persistent lymph-node enlargement was most likely vaccine-related. MRI did not show gross invasive breast cancer.

Because the DCIS involved a large area of the breast, she underwent a total left mastectomy with sentinel lymph node removal and immediate DIEP-flap reconstruction. Final pathology showed multifocal intermediate-grade DCIS that was estrogen- and progesterone-receptor positive. The sentinel node was negative for malignancy. She recovered without complications and did not receive additional cancer treatment.