Mammary and extramammary Paget's disease. An immunocytochemical study.

The localization and distribution of human casein has been investigated in 20 patients with Paget's disease (16 with the mammary and 4 with the extramammary form) by means of immunofluorescence and immunoperoxidase techniques. This milk protein has been detected in neoplastic cells in intraductal carcinomas of the nipple and in intraepidermal cells identifiable as Paget cells. The degree of the staining varied in different cells of the same case and in different cases. Some casein-containing intraepidermal cells, as revealed by immunofluorescence, could not be recognized after retaining of the sections as Paget cells: they could not morphologically be distinguished from other basally located epidermal cells. This finding raises the question of the existence of "pre-Paget" cells. The results obtained are discussed in relation to theories on the origin and nature of Paget cells. The immunocytochemical methods for casein detection might also be find possible application in the diagnosis of Paget's disease.