Heterogeneous distribution of actin, myosin, fibronectin and basement membrane antigens in primary and metastatic human breast cancer

The distribution of actin, myosin, fibronectin and basement membrane antigens has been studied by indirect immunofluorescence in benign and malignant human breast lesions. While benign tumors showed only minor differences from normal mammary tissue, tumors of different histological types displayed a heterogeneous distribution of the antigens studied. Heterogeneity was observed within the same tumor, among different neoplasms and between primary tumors and autologous metastases. As a common characteristic, most of the tumors did not stain for actin and myosin, the pattern being similar to that found in myoepithelial cell distribution. In transformed epithelia there was often a lack of detectable actin with a myosin-positive fluorescence. Staining for both proteins was diffused to most of the cell cytoplasm. Staining for fibronectin was seen in only a minority of the cases, with medullary tumors being the most positive. Basement membrane stain was either absent or decreased and fragmented, except in rare ductal, i.e. papillary, carcinomas. Medullary tumors displayed an almost continuous, though fragmented basement membrane in approximately 70% of cases.