While occasional scattered<unk>  cell formation occurs with considerable frequency in lung carcinomas, this is not considered to be of clinical significance. According to current classification criteria, a tumor can only be diagnosed as LCLC-RP when an undifferentiated<unk> -cell lung carcinoma contains a<unk>  cell component that makes up at least 10% of the tumor mass. Microscopic characteristics of<unk>  cells include: *Oval to polygonal cell shape *Eosinophilic, hyaline-like perinuclear agglomerations of intermediate filaments *Compressed, eccentric nuclei *Prominent central macronucleoli (one or two) *Abundant eosinophilic cytoplasm *Reticular chromatin pattern Differential Diagnosis The differential diagnosis of LCLC-RP includes secondary metastatic lesions, malignant melanoma of the lung with<unk><unk> , mucinous adenocarcinomas (particularly those featuring signet-ring cells), rhabdomyosarcoma, epitheloid angiosarcoma, pleural mesothelioma, and plasmacytoma. Imaging On radiological imaging, most cases of LCLC-RP are single "coin lesions" or discrete masses, but cases presenting as multiple nodules throughout the lung have also been noted. Cases with inhomogeneous-appearing consolidation on CT have been reported, as well as aerogenous, lepidic-type spread. Some<unk> , centrally located LCLC-RP have been noted to show signs of gross necrosis and cavitation on imaging studies, as well as being associated with the presence of<unk>  bullae. Immunohistochemistry Immunohistochemistry is an important factor in diagnosis. Results of immunohistochemistry (IHC) staining in<unk>  lung cancers tends to reflect the multiphasic nature of these tumors. Typically, markers expressed in LCLC-RP include those seen in "generic" NSCLC's, such as epithelial membrane antigen (EMA, 61%), various cytokeratins (CK's, 80%), and markers associated with the underlying "parent" pulmonary carcinoma. Expression of immunomarkers in the<unk>  cells, however, have often been noted to be weaker and more diffuse than those in the more differentiated tumor cells. They also more frequently express "non-carcinomatous" markers typically associated with "dedifferentiated" neoplasms. Expression of thyroid transcription factor-1 (TTF-1), a commonly used marker for primary lung cancers, appears to be less frequent in<unk>  carcinomas than in most other histotypes of pulmonary cancers. Vimentin, an intermediate filament protein usually found in sarcoma, is ubiquitously (nearly 100%) expressed diffusely throughout the cytoplasm of the<unk>  cells, and is often intermingled with CK's in their whorled inclusions. Some studied have reported that neuroendocrine-related markers (i.e. neuron-specific enolase (NSE), neural cell adhesion molecule (NCAM), chromogranin A (CgA), synaptophysin), are also quite frequently expressed in a significant proportion of<unk>  cells.
Large-cell lung carcinoma with rhabdoid phenotype
Epithelial-myoepithelial carcinoma of the lung
Salivary gland–like carcinoma of the lung
Mucinous cystadenocarcinoma of the lung
Basaloid large cell carcinoma of the lung
Large cell neuroendocrine carcinoma of the lung
Plexiform angiomyxoid myofibroblastic tumor
Atypical pulmonary carcinoid tumour