What happened, in summary

A 73-year-old woman had previously been treated for left breast invasive ductal carcinoma with partial mastectomy and adjuvant radiation. As she finished radiation, a small lump became palpable in the upper outer right breast where a simple cyst had been followed.

Ultrasound showed that the cyst had developed vascular mural nodularity and now measured 1.6 × 1.1 × 1.2 cm. Core biopsy found well-differentiated invasive ductal carcinoma, grade 1, with extensive intracystic ductal carcinoma in situ. The new right-breast tumour was more than 95% estrogen-receptor positive and more than 95% progesterone-receptor positive, HER2 negative, with a Ki-67 index of 11–50%.

She underwent needle localization, right partial mastectomy and sentinel lymph-node biopsy. Final pathology showed a 0.5 × 0.3 × 0.3 cm invasive ductal carcinoma and a 0.6 cm focus of ductal carcinoma in situ. Surgical margins were clear and the sentinel lymph node showed no metastasis.

She then completed radiation therapy to the right breast and started anastrozole 1 mg daily, with a plan to continue endocrine therapy for 5 years. Her earlier left-breast cancer remained an important part of her history, while the new treatment course addressed the separate right-breast primary.