The term
thyroid tumours of uncertain
malignant potential (TT-UMP) has been proposed for a subgroup of follicular-patterned
thyroid tumours for which benignancy or malignancy cannot be assessed with certainty. The
frequency, diagnostic
reproducibility,
immunohistochemistry and
molecular genetic profiling of such
tumours have been poorly explored. We, therefore, investigated (1) the
frequency of TT-UMP diagnosed in a single institution (Nice, France: 2004-2008), (2) the observer variation among four
pathologists, (3) whether
immunohistochemical and
molecular genetic profiling of TT-UMP provide additional information concerning such
lesions. A series of 31 diagnosed TT-UMP (2.9%) out of 1,078 consecutive thyroidectomies were analysed. It comprised 15 follicular
thyroid tumours of UMP (FT-UMP) and 16 well-differentiated
tumours of UMP (WDT-UMP). Observer concordance was 70% for all TT-UMP. More than 50% of FT-UMP expressed galectin-3 and CK19, whereas more than 50% of WDT-UMP expressed HBME-1. Five cases of TT-UMP showed N-RAS
mutations, while one showed H-RAS
mutation and another
PAX8/PPARgamma
rearrangement. In conclusion, the
frequency of TT-UMP is low in our institution. Diagnostic
reproducibility is within the same range as other published data on follicular-patterned
thyroid tumours. The ancillary methods have a low impact on aiding diagnosis of such
lesions.
