[Development and neoplastic progression of benign and malignant cutaneous cylindroma]

Cylindromas of the skin are subjected to a constant biological evolution in their growth and differentiation, leading in rare instances to metaplasia or even in true malignancy. By using optical microscopy and autohistoradiography after incorporation of tritiated thymidine and proline, several stages of neoplastic progression can be recognized such as growth, primary involution, inflammatory regression and malignant transformation. The stage of growth is characterized by low proliferative indices in clear cells of the lobules while dark cells are almost not dividing. Primary involution consists of massive accumulation of basement membrane components accompanied by lysis of cells. Inflammatory regression results from the infiltration of the neoplasm by lymphocytes with disappearance of the basement membrane. Malignant transformation appears to be multifocal.