Since, first, MMP1 processing is in part dependent on MMP3, second, these MMPs present partially distinct substrate specificities, and, third, none of their tissue inhibitors was found over-expressed, concomitant increases of MMP1 and MMP3 in patients' fibroblasts strongly argue for a prominent role of the mesenchyme in BCC development and invasiveness in NBCCS. The gene discussed is MMP1; the disease is skin basal cell carcinoma.