THE ORIGIN OF THE MYOFIBROBLASTS IN BREAST-CANCER - RECAPITULATION OFTUMOR ENVIRONMENT IN CULTURE UNRAVELS DIVERSITY AND IMPLICATES CONVERTED FIBROBLASTS AND RECRUITED SMOOTH

The origin of myofibroblasts in stromal. reaction has been a subject o f controversy. To address this question definitively, we developed tec hniques for purification and characterization of major stromal cell ty pes. We defined a panel of markers that could, in combination, unequiv ocally distinguish these cell types by immunocytochemistry, iso-electr ic focusing, immunoblotting, and two-dimensional gel electrophoresis. We then devised an assay to recapitulate in culture, within two weeks of incubation, critical aspects of the microenvironment in vivo includ ing the typical tissue histology and stromal reaction. When confronted with tumor cells in this assay, fibroblasts readily converted into a graded pattern of myogenic differentiation, strongest in the immediate vicinity of tumor cells. Vascular smooth muscle cells (VSMC), in cont rast, did not change appreciably and remained coordinately smooth musc le differentiated. Midcapillary pericytes showed only a slight propens ity for myogenic differentiation. Analysis of ten primary tumors impli cated converted fibroblasts (10/10), vascular smooth muscle cells (4/1 0), and pericytes (1/10) in the stromal reaction. Tumor cells were sho wn to specifically denude the venules both in culture and in vivo, exp laining the VSMC phenotype in the stroma. The establishment of this as say and clarification of the origin of these cells pave the way for fu rther analysis of the mechanisms of conversion, and of the consequence of such heterogeneity for diagnosis and treatment.