Absence of neuroendocrine cells in fetal and adult mammary glands. Are neuroendocrine breast tumours real neuroendocrine tumours?

Some human breast carcinomas show features of neuroendocrine differentiation. The histogenesis of these tumours is debated especially because of the difficulty in locating neuroendocrine cells in normal mammary glands. The aim of this study was to search for neuroendocrine cells in two series of adult and fetal normal mammary glands. Eight female fetus breasts of gestational age between 24 and 37 weeks and 27 cases of normal adult breast tissues were investigated. Paraffin sections of formalin fixed samples were studied by Grimelius stain and immunohistochemistry using the monoclonal antibody anti-chromogranin A. An ultrastructural study was performed on a fetal mammary gland at the 37th week of gestation. Our results showed no histochemical, immunohistochemical and ultrastructural evidence of neuroendocrine differentiation in normal cells of fetal and adult mammary glands. The absence of neuroendocrine cells during mammary gland development indicates that the neuroendocrine part of a mammary cancer does not originate from a normal counterpart but that it is the result of a neuroendocrine differentiation during neoplastic progression.