Metaplasia. An overview.

Metaplastic changes are common lesions found at widespread locations, occurring in both reactive and neoplastic tissues. Metaplasia has the following characteristics: (1) it can arise not only as a proliferation and transformation of immature (stem) cells, but also as a direct or indirect transformation of mature cells; (2) through metaplasia, a given cell may exhibit epithelial, mesothelial, or mesenchymal characteristics, regardless of the tissue of origin; and (3) its importance lies in that metaplastic changes can often be symptomatic and may simulate tumors clinically, grossly, or histologically.