Primary lesions that may imitate metastatic tumors histologically: A selective review

Several primary pathologic entities in diverse anatomic locations have the potential to simulate metastatic neoplasms histologically. Their misinterpretation as such may result in needless and extensive clinical evaluations that are intended to detect a presumed malignancy at another site. More importantly, mistakes of this type can deprive patients of surgical excisions that could be curative. This presentation considers a review of selected primary lesions that can simulate metastases. They include hemangioblastoma, glioblastoma and meningioma with epithelial metaplasia, choroid plexus carcinomas, primary neuroendocrine carcinomas in unusual locations, special forms of sinonasal and salivary glandular adenocarcinoma, clear-cell thyroid carcinomas, unusual microscopic subtypes of pulmonary adenocarcinoma, epithelioid myomelanocytomas ("sugar tumors"), mesotheliomas, primary thymic carcinomas, endodermal choristomas of the interatrial myocardium, peripheral cholangiocarcinoma, adrenocortical carcinoma, adenocarcinomas of the urinary bladder, mucinous and "rhabdoid" tumors of the ovaries, rete testis adenocarcinomas, interdigitating dendritic-cell sarcoma of lymph nodes, selected sweat gland carcinomas, cutaneous Merkel cell carcinoma, primary dermal and subcutaneous melanoma, mucosal and visceral melanomas, epithelioid sarcoma, clear-cell sarcoma, and adamantinoma of long bones. Differential diagnostic observations are emphasized in reference to those lesions.