It has become clear that the initiation and progression of carcinomas depend not only on alterations in epithelial cells, but also on changes in their microenvironment. However, the functional interplay between carcinomas and their stoma is still poorly understood. In this report Hawsawi and colleagues present clear evidence that breast carcinoma–associated fibroblasts (CAFs) and their tumor counterpart fibroblasts (TCFs) present tumor-associated features. Using the immunohistochemistry technique, it has been shown that while normal breast fibroblasts (NBFs) from plastic surgery do not express the a-smooth muscle antigen (a-SMA), both CAFs and TCFs from the same patients are positive for this antigen and, therefore, are myofibroblasts (bottom panel, lower row). Also using immunohistochemistry, the authors show that Ki-67 protein is highly expressed not only in epithelial cells, but also in their corresponding stromal fibroblasts from the same tissue (top panel). The expression of Ki-67 in both cell types suggests that the increase in the proliferation rate is not restricted to breast carcinomas but is present in their stromal fibroblasts as well, which may enable tumor cells to grow and spread. In addition, using the two-dimensional gel electrophoresis technique, it has been shown that CAF, TCF, and NBF cells present different proteome profiles, with many proteins differentially expressed between these cells (bottom panel, upper row). Thisindicates that breast CAFs and their corresponding adjacent counterparts present different genetic alterations that need to be identified and characterized in order to further comprehend the role of stromal fibroblasts in the development and spread of breast cancer. Further characterization is also required for the development of novel therapeutic approaches that specifically target these cells to improve the treatment ofdifferent types of carcinoma. For details, see the article by Hawsawi and colleagues on page 2717 of this issue.