The Role of Postmastectomy Radiotherapy in Locally Advanced Breast Cancer After Pathological Complete Response to Neoadjuvant Chemotherapy.

The Case A previously healthy woman, aged 32 years, presented to the oncology clinic with a 6-month history of left-breast tumor, mastalgia, and swollen axillary nodes. Physical examination was relevant for a 6-cm palpable mass in the upper outer quadrant of the left breast and an ipsilateral 2-cm, nonfixed axillary lymph node. Mammography showed a 1-cm mass in the upper outer quadrant, a 5.2-cm mass in the lower outer quadrant, and enlarged pathologic lymph nodes (BI-RADS category 5 disease). Breast ultrasound revealed 3 axillary lymph nodes with cortical thickening and loss of normal morphology (the largest with a 2.6-cm length in the long axis) (Figure 1A-B). The breast´s core biopsy revealed a grade 3 apocrine invasive carcinoma with lymphovascular invasion; immunohistochemistry testing showed HER2-negative, hormone receptor-negative disease (estrogen receptor, 0%; progesterone receptor, 0%; HER2-negative, Ki67, 50%) (Figure 2A-B). A fine-needle aspiration biopsy of the axillary lymph nodes showed invasive breast carcinoma as well. Bone scintigraphy and a chest/abdomen CT scan ruled out metastatic disease. Upon initial diagnosis, clinical stage was deemed as cT3N1M0 (American Joint Committee on Cancer 8th edition: anatomic stage IIIA, clinical prognostic stage IIIC). After a multidisciplinary tumor board discussion, the patient underwent neoadjuvant chemotherapy with weekly paclitaxel, followed by 4 cycles of dose-dense doxorubicin plus cyclophosphamide. After completing neoadjuvant treatment, clinical examination was relevant for a residual 1-cm palpable left breast mass and no palpable axillary nodes. Mammography and breast ultrasound showed a 77% partial response in the primary tumors, and axillary nodes with normal morphology and size (Figure 1C-D). Due to multicentric tumor disease, breast-conserving surgery would not confer satisfactory cosmetic results on her, and a modified radical mastectomy with intraoperative sentinel lymph node biopsy (and second-stage breast reconstruction) was planned. However, during surgery, the surgeons failed to identify the mapped lymph node, and level I-III axillary lymph node dissection was performed. The pathology report described complete pathological response: Miller and Payne criteria grade 5 response with the absence of malignant cells within the mastectomy specimen and in 24 lymph nodes (Figure 2C-E). Pathological staging after neoadjuvant treatment concluded ypT0N0M0 disease. Subsequent treatment for this patient was discussed in another tumor board.