Should response to preoperative chemotherapy affect radiotherapy recommendations after mastectomy for stage II breast cancer?

A healthy 38-year-old woman presents with a palpable mass at the two o’clock position of the left breast. Mammography discloses a 3.2-cm spiculated lesion corresponding with the palpable abnormality, and ultrasonography confirms a solid mass in the breast and an enlarged, 2.1-cm lymph node with a thickened cortex in the ipsilateral axilla. Ultrasound-guided core needle biopsy of the breast mass diagnoses an invasive ductal carcinoma, poorly differentiated (grade 3), with lymphovascular invasion. Lymph node fine-needle aspiration is positive for malignant cells. Immunohistochemical studies on the breast specimen indicate that the tumor is triple negative, lacking estrogen and progesterone receptors and human epidermal growth factor 2 expression. The patient receives preoperative chemotherapy with doxorubicin and cyclophosphamide followed by paclitaxel. She has a dramatic clinical response; the breast and axillary masses shrink rapidly with chemotherapy. At the time of mastectomy, she is found to have several foci of residual invasive cancer in the breast (largest focus, 0.3 cm), located in a 3-cm tumor bed showing treatment effect (Figs 1A to 1C). The margins are negative, as are all 11 axillary lymph nodes. Her pathologic response to neoadjuvant treatment is judged Miller-Payne grade 4. She is referred for consideration of postmastectomy irradiation.