Breast cancer is a common disease in females but very rare in males, in whom it shows a more metastatic behavior, and a worse prognosis. Matrix metalloprotease-2 (MMP-2) and MMP-9 are proteolytic enzymes balanced by tissue inhibitor of MMP-2 (TIMP-2), commonly involved in cancer metastasis. This is the first study on gelatinolytic activity in male breast cancer patients, compared to that in female patients. In cancer tissues, both gelatinases were more expressed than in normal samples, being and more concentrated in male than in female patients. TIMP-2 levels were slightly increased in normal compared to those in cancer tissues and more concentrated in males than in females. Immunostaining showed that in male cancer tissues MMP-2 and MMP-9 staining was more intense and diffuse than in female cancer tissues, while no differences were observed regarding TIMP-2. In conclusion, the increased expression of gelatinases in male breast cancer patients together with anatomical features might explain the high tendency toward metastasis and the worse prognosis. (C) 2002 Elsevier Science (USA).