Background: Thrombospondin (TSP), a cell-matrix adhesion protein, and cysteine-serine-valine-threonine-cysteine-glycine (CSVTCG), a major TSP cell adhesive domain, have recently been shown to play a role in tumor cell metastasis. In this study we immunohistochemically localized TSP and its newly discovered CSVTCG-specific receptor in normal, benign, and neoplastic breast tissues.
Experimental design: Paraffin sections of normal, benign, and neoplastic breast tissue were examined immunohistochemically for the presence of TSP and its CSVTCG-specific receptor using the avidin-biotin complex immunoperoxidase staining procedure.
Results: Positive staining using polyclonal antibodies for TSP and its tumor cell adhesion receptor, isolated from a human adenocarcinoma of the lung, was observed in all primary breast ductal carcinomas examined (N = 11). In contrast, all benign lesions and normal breast tissue stained negative for TSP and its receptor with the exception of two fibrocystic breast samples with hyperplasia. One of the samples showed strong TSP staining of ductal apocrine cells, whereas the other showed apical receptor staining of hyperplastic ductal cells. The negatively staining normal and benign tissues consisted of 1 normal breast, 1 gynecomastia, 5 fibroadenomas, and 6 fibrocystic samples. Positive staining for TSP in ductal carcinoma was only localized in the dense stromal collagen adjacent to tumor, whereas the TSP receptor localized to the tumor cells. Consistent with these immunohistochemical staining results was the observation that protein extracts of breast carcinoma cells contained receptor with no detectable TSP as revealed by Western blotting. Capillary endothelium was focally positive for receptor in regions proximal to ductal epithelium in 8 of 11 neoplastic tissues and in 6 of 14 benign samples.
Conclusions: Our results indicate that increasing expression of stromal TSP and the CSVTCG-specific TSP receptor in ductal epithelium correlates with neoplastic transformation. In addition, our results indicate that both malignant and benign breast tissue can stimulate surrounding capillaries to express the TSP receptor, whereas only carcinoma has the capacity to stimulate surrounding nonendothelial stromal cells, such as myofibroblasts, to secrete a TSP-rich matrix that may contribute to the desmoplastic stromal reaction characteristic of ductal carcinoma tumor. The TSP-rich matrix may then promote tumor cell attachment, migration, and angiogenesis, factors important in tumor growth. The receptor-rich capillary endothelium may promote the cell adhesive interactions important in tumor intravasation. Taken together the results of this study provide a rational basis for a role of TSP in tumor angiogenesis and metastasis.