Fig. 5.

Metastatic residual carcinoma in a lymph node with histologic features indicative of tumor regression: in low-power view, an axillary lymph node shows lymphocyte depletion, fibrosis, and aggregation of foamy histiocytes (green circle, A), which we suggest are histologic features indicative of tumor regression due to neoadjuvant therapy. In high-power view, metastatic tumor cell clusters are identified in a regressed lymph node (arrows, B). Immunohistochemistry for cytokeratin is helpful to identify metastatic tumor cell clusters in a regressed lymph node (C, D).