Transmission electron microscopy of fine needle aspiration biopsies of metastases: Accuracy of both techniques as established by biopsy diagnoses

To determine the accuracy of fine needle aspiration biopsy in establishing the primary on cytology and on cytologic and electron microscopy examinations using tissue biopsy as the gold standard. A retrospective study of 96 nonrandomly selected cases of metastases with an unknown primary was carried out. Tissue biopsy was performed subsequently for confirmation. Proper clinical correlation was part of the analysis. The accuracy of cytology in identifying the tumor category (e.g., carcinoma, sarcoma) and tumor type (e.g., adenocarcinoma, leiomyosarcoma) was 76% and 78%, respectively, while that of electron microscopy was 95% and 91%, respectively. The primary site was correctly identified by cytology in 59% and by electron microscopy in 88% of cases, provided that clinical parameters were also considered. Electron microscopy is an ancillary technique useful in increasing the accuracy of tumor classification of metastatic neoplasms identified by fine needle aspiration biopsy.