Reliable identification of small cell lung cancer in cytological specimens by immunocytology

A reliable diagnosis of small cell lung cancers (SCLC) is of high clinical relevance. We investigated whether immunocytology substantially improves the diagnostic accuracy of conventional cytology in diagnosing SCLC.

162 carcinomatous specimens clinically suspected to originate from pulmonary neoplasms were investigated by cytology and immunocytology. Immunocytology was performed on smears using HEA125 and pancytokeratin antibodies as epithelial markers and MOC-1 as SCLC probe.

As histologically clarified, 114 specimens corresponded to pulmonary neoplasms (SCLC = 51; non-small cell lung cancer: NSCLC = 59; mixed SCLC/NSCLC = 2; carcinoid = 2), 48 to nonpulmonary adenocarcinomas. By conventional cytology tumor cells were clearly detected in 93 (57.4%) and suspected in another 43 (26.5%) cases (83.9% overall sensitivity). Considering SCLC samples, tumor cells were diagnosed or suspected in 36 (70.5%), not identified in 10 (19.6%), and misdiagnosed as hematological malignancy in 5 cases. Only 2 specimens were accurately diagnosed as SCLC. Using the epithelial antibodies all samples were identified as carcinomatous. MOC-1 stained all but one SCLC, both SCLC/NSCLC, and both carcinoids. One SCLC brush smear was MOC-1 negative, containing only squamous epithelium. 3 pulmonary adenocarcinomas stained falsely positive, all nonpulmonary carcinomas MOC-1 negative.

Immunocytology substantially improves the diagnostic accuracy of cytology in diagnosing SCLC with a diagnostic sensitivity of 98% and specificity of 97%.