HER2-positive squamous cell breast cancer in complete remission

What happened, in summary

A 45-year-old Chinese woman noticed a painless mass in the upper inner quadrant of her right breast. On examination, the lump was firm, tender, uneven, poorly mobile, and not attached to the chest wall or skin. Imaging showed an irregular breast lesion measuring about 2.4 cm, classified as BI-RADS 4C, along with a right axillary lymph node that appeared enlarged but retained hilar structure. CT showed no other space-occupying lesions in the chest or abdomen. No abnormal changes were seen in the left breast or left axillary nodes. She underwent modified radical mastectomy with right axillary sentinel lymph node dissection. Pathology showed primary squamous cell carcinoma of the breast. The tumor had malignant squamous features with intercellular bridges, keratin-pearl formation, and squamoid nests. No invasive ductal carcinoma component, spindle-cell component, mesenchymal differentiation, skin involvement, or nipple involvement was identified. Immunohistochemistry showed CK5/6 positivity, p53 positivity, p63 positivity, HER2 positivity, ER negativity, PR negativity, and PD-L1 negativity, with Ki-67 at 40%. HER2 was scored 2+ by IHC, and FISH confirmed HER2 gene amplification with a HER2/CEP17 ratio of 2.72. No metastatic cancer cells were found in the axillary lymph node. She was classified as Stage IIA breast cancer, T2N0M0. After surgery, she received 4 cycles of doxorubicin plus cyclophosphamide every 21 days, followed by 4 cycles of docetaxel plus trastuzumab every 21 days. She then continued maintenance trastuzumab plus pertuzumab every 3 weeks. Nausea and vomiting occurred during treatment, with no unexpected adverse events. Clinical follow-up showed complete remission and survival beyond 4 years.