To obviate the difficulty of ruling out confounding variables (eg, age, individual variability) as the source of differences seen when comparing tumor tissue and control tissue from unrelated individuals, we examined the expression of matrix metalloproteinase (MMP)-1 (interstitial collagenase) and MMP-9 (92-kDa gelatinase B) in histologically normal skin immediately adjacent to basal cell carcinomas (peritumoral tissue) after Mohs micrographic surgery and postauricular skin from the same patients. Design: Peritumoral and postauricular skin samples were obtained from 17 patients undergoing Mohs surgery. Expression of MMP-1 and MMP-9 was examined in these specimens using a combination of approaches including zymography, collagen-degradation assays, and immunohistology. Results: The expression levels of MMP-1 and MMP-9 were consistently elevated in the peritumoral tissue compared with skin from the distal site. Conclusion: This finding indicates that even when potentially important variables such as age and individual variability are controlled for, tumor-specific effects on the expression of MMP-9 and MMP-1 remain.

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