Background: Matrix metalloproteinases (MMPs) are proteolytic enzymes which degrade extracellular matrix and basement membrane. There is much evidence that their increased expression is correlated with tumor aggressiveness in various carcinomas. Tissue inhibitor of metalloproteinases (TIMPs) are the specific inhibitors of MMPs. MMPs and TIMPs are considered to play an important role in carcinoma invasion and metastasis. We hypothesized that MMPs and TIMPs also play an important role in thymoma.
Materials and methods: This study included 34 thymoma cases. The mRNA levels of MMP-1, -7, and -9, TIMP-1 and -2, and GAPDH were quantified by real-time polymerase chain reaction using LightCycler. We also performed immunohistochemistry for TIMP-1.
Results: The TIMP-1/GAPDH mRNA expression level was significantly higher in invasive (stage II-IV) thymomas (means +/- SE, 81.4 +/- 28.1) than in noninvasive (stage I) thymomas (30.9 +/- 8.3, P = 0.026). The MMP-1/GAPDH mRNA expression level was also higher in invasive thymomas (19.7 +/- 7.5) than in non invasive thymomas (2.26 +/- 1.72, P = 0.020). Immunopositivity of TIMP-1 was localized in stromal cells adjacent to the advancing margin of the tumor.
Conclusions: These findings suggest that TIMPs and MMPs play an important role in the invasion of thymoma.