Atypical endocrine tumors of the lung.

Seven malignant peripheral lung tumors that were diagnosed using light microscopy as large-cell carcinomas or as epidermoid or adenocarcinomas were studied by light and electron microscopic histochemistry. All tumors contained numerous dense-core granules. The cells were joined by desmosomes and contained well-developed tonofilament bundles. Serotonin was demonstrated in six of seven tumors and argyrophilic granules were demonstrated in five of six tumors tested. Four tumors produced mucus. All tumors extended to the visceral pleura and two invaded the chest wall. The existence of lung tumors that contain serotonin and bear argyrophilic putative endocrine granules, but that do not have a light-microscopic histology characteristic of either carcinoid or oat-cell carcinomas, is confirmed. The presumptive endocrine nature of such tumors usually passes unrecognized because they lack criteria to allow diagnosis by routine methods.