Immunostaining for Met/HGF receptor may be useful to identify malignanciesin thyroid lesions classified suspicious at fine-needle aspiration biopsy

The receptor for hepatocyte growth factor (Met) is not expressed in the nor mal thyroid but it is overexpressed in most thyroid carcinomas. We evaluate d whether Met immunostaining of cytological smears from fine-needle aspirat ion biopsy (FNAB) may be useful for the preoperative diagnosis of thyroid c ancer. Notably, routine cytological examination often fails to distinguish well-differentiated follicular carcinomas and a proportion of papillary car cinomas (low-grade papillary carcinomas and papillary carcinomas follicular variant [FVPTC]) from benign lesions: all these lesions are usually classi fied as suspicious. We examined 80 thyroid lesions diagnosed as suspicious at cytology that had subsequently undergone surgery. The histologic diagnos is had been: papillary carcinomas (n = 14), FVPTC (n = 11), follicular carc inomas (n = 5), atypical follicular adenomas (n = 5), follicular adenomas ( n = 20), and nodular goiters (n = 5). We also studied typical papillary car cinomas (n = 30) and nodular goiters (n = 10), all correctly diagnosed at c ytology. In lesions classified suspicious at routine cytology, Met immunost aining was positive in 12 of 14 (85.7%) papillary carcinomas, 8 of 11 (72.7 %) FVPTC, 7 of 25 (28%) follicular carcinomas, and 5 of 5 atypical adenomas . In contrast, none of the 25 lesions cytologically, suspicious but benign at histology were positive. These data suggest that Met immunostaining of s uspicious cytological smears are useful for identifying malignant lesions, especially those with a papillary histotype.