Progesterone receptor immunoreactivity in minute meningothelioid nodules of the lung.

Meningothelioid nodules (MNs) are not uncommon lesions of the pulmonary interstitium composed of monomorphic round to spindle cells, likely reactive in nature. Their origin is unsettled, though a derivation from arachnoid-like cells in conditions of perturbed perfusion of the pulmonary tissue has been proposed. Here we confirm the consistent occurrence of intense progesterone-receptor immunoreactivity in MNs fortuitously detected in surgical specimens of lung carcinomas. This finding corroborates the view that these proliferations exhibit arachnoid cell-like differentiation and suggests a role for sex-steroid hormones in the control of their growth.