To investigate the invasive activity of thyroid cancer, an in situ hybridization study was carried out in 19 thyroid tumors, including nine papillary carcinomas, five follicular carcinomas and five follicular adenomas, by using a 35S-labeled MMP-1 (matrix metalloproteinase-1) cDNA probe. The MMP-1 gene was expressed not in the cancer cells but in the fibrous capsules of papillary carcinoma. Thyroid cancer is generally circumscribed by a fibrous capsule. We found that types I and III collagen constitute the fibrous capsule, and that the MMP-1 gene was expressed in the outer border of these sites. These findings suggest that MMP-1 plays an important role in the invasion of thyroid cancer.
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