[The tumorlet carcinoid in bronchiectasis-changed lungs. An example of a multifocal, endocrine tumor].

Tumorlets of the lungs are multifocal hyperplasias of endocrine cells which may develop via nodular hyperplasia into peripheral, occasionally also metastatic, carcinoids. They are observed with a particular frequency in bronchiectasis. Resected material obtained from patients with bronchiectasis (4 women, 3 men, mean age 43.5 years, range 19-66 years) were submitted to conventional histological studies employing HE, PAS and van Gieson staining, and also to an immunohistological analysis. Conventional staining sufficed to identify endocrine cell proliferations in the scarred lung tissue in 3 preparations. An assignment to bronchioles and alveoli with conventional histology was, in view of the extensive scarring of the lung parenchyma, very difficult, but was accomplished with the aid of immunohistological investigation. As a multifocal tumour, the tumourlet suggests itself as a model, employing immunohistochemistry, for studying the formal genesis of neuroendocrine tumours of the lung, since it shows the earliest intra-epithelial neoplastic transformations through in situ tumour to carcinoid.