HER2-positive breast cancer: surgery after neoadjuvant therapy

What happened, in summary

This 62-year-old woman had calcifications found in the 12:00 axis of the right breast on screening mammogram. Stereotactic biopsy showed several foci of invasive ductal carcinoma along with high-grade ductal carcinoma in situ. The tumor was clinical Stage I, T1N0M0, measuring about 0.8 cm. Biomarker testing showed ER 1% weakly positive, PR-negative, and HER2-positive with 3+ staining by immunohistochemistry. Her case was reviewed at a multidisciplinary tumor board during the COVID-19 pandemic, when operating-room access was delayed. To bridge safely to surgery, the team started neoadjuvant ado-trastuzumab emtansine, also called T-DM1, at 3.6 mg/kg IV every 3 weeks for 6 cycles. When operating rooms reopened, she underwent right breast lumpectomy with sentinel lymph node biopsy. Surgical pathology showed no residual invasive or in situ carcinoma and negative sentinel nodes, confirming a pathologic complete response. After surgery, she received adjuvant radiotherapy to 40 Gy. Because the cancer was HER2-positive, she also received trastuzumab 6 mg/kg IV every 3 weeks for 11 cycles. Because ER staining was weakly positive, she started anastrozole 1 mg daily as endocrine therapy. Her story differs from other patients in the same series because she was one of the patients who responded well to neoadjuvant T-DM1 rather than progressing during the surgical delay. On follow-up, she remained on anastrozole and had no evidence of disease. This response supports the use of T-DM1 as a temporary bridge in selected HER2-positive early breast cancers when surgery must be delayed, while still requiring close monitoring for progression.