HBME-1 IMMUNOSTAINING IN THYROID FINE-NEEDLE ASPIRATIONS - A USEFUL MARKER IN THE DIAGNOSIS OF CARCINOMA

The monoclonal antibody, HBME-1, generated against the microvillous su rface of mesothelial cells, has been shown to have significant reactiv ity in histologic sections of follicular-derived thyroid malignancies. We examined the diagnostic utility of HBME-1 in thyroid fine-needle a spiration (FNA) specimens. Twenty-four aspirates from 23 patients were evaluated. Only cases with adequate cell blocks and tissue follow-up were studied. Immunocytochemical analysis was performed on air-dried, direct smears and on sections from Bouin's-fixed, paraffin-embedded ce ll blocks with a standard avidin-biotin peroxidase complex method with epitope retrieval. The same immunostaining technique was applied to t he corresponding formalin-fixed tissue sections. Eight (57%) of the 14 malignant aspirates showed strong cytoplasmic and/or membrane immunor eactivity for HBME-1. The cell-block and direct-smear preparations wer e positive in five of seven papillary carcinomas (one follicular varia nt), one of one minimally invasive follicular carcinoma, and one of fo ur hybrid tumors with mixed papillary and follicular features. An addi tional hybrid tumor case was focally positive only in the smear slide, The eighth positive case was an adenosquamous carcinoma of the larynx that invaded into the thyroid (smear preparation was negative for thi s case) The 10 benign lesions were negative. All of the malignant-tumo r tissue sections were positive for HBME-1, and focal positivity was s een in 5 of 10 benign resection specimens. We conclude that a positive immunostain for HBME-1 on a thyroid FNA is supportive evidence that t he lesion is a carcinoma, that a negative result for HBME-1 does not p reclude the diagnosis of thyroid carcinoma, and that HBME-1 can be eff ectively applied to thyroid FNA specimens and can be a valuable adjunc t in the cytologic diagnosis of thyroid malignancies.