Figure 4

Immunohistochemical staining for α-smooth muscle actin in metastases of human breast cancer to (a) bone marrow, (b) liver, (c) lymph node, and (d) pleura. In all of the cases that we examined, there was extensive infiltration of the tumor metastases by myofibroblasts (brown stain). Note that the myofibroblasts appeared to be in direct contact with nearly all of the tumor cells in these sections. Even very early micrometastases (defined as fewer than 100 tumor cells) of well differentiated tumors to lymph nodes (panel c) and larger metastases of poorly differentiated tumors (panel d) were in very close proximity to myofibroblasts. Serial sections of the same tissues did not stain for CD10 or smooth muscle myosin heavy chain (not shown), thereby confirming that the cells are myofibroblasts rather than myoepithelial cells. Hematoxylin counter-stain was used.