Mucoepidermoid carcinoma of the thyroid: a report of three cases and postulated histogenesis.
BACKGROUND
Primary mucoepidermoid carcinoma (MEC) of the thyroid is a rare clinical and pathological entity that accounts for <0.5% of all thyroid malignancies. Although the histogenesis has been controversial, most investigators now favor it as arising from either metaplasia of thyroid follicular epithelium or heterologous de-differentiation from papillary thyroid carcinoma (PTC). We report three cases of thyroid MEC found in continuity with, and clearly arising from de-differentiation of, well-differentiated thyroid carcinomas (WDTCs).
The cases presented here included two women (aged 22 and 52) and one man (aged 58). One of these cases arose in conjunction with PTC, one with follicular thyroid carcinoma (FTC), and one with Hurthle cell carcinoma (HCC). In all three cases, there was a gradual transition in morphology between the areas of typical WDTC and the areas showing MEC differentiation. In addition, immunohistochemistry demonstrated a gradual loss of thyroid specific markers (thyroid transcription factor-1, thyroglobulin) mirroring the change in morphology.


CONCLUSIONS
We conclude that thyroid MEC can arise from metaplastic de-differentiation of WDTC, including FTC or HCC in addition to PTC. Currently, we recommend that after excision, each of the WDTC and MEC components of these tumors be treated with targeted adjuvant therapies, which may involve radioactive-iodine ablation, thyrotropin suppression, and external beam radiotherapy.
Department of Endocrine and Oncology Surgery, Royal North Shore Hospital, Sydney, Australia.
Ruth S
RS
Prichard
James C
JC
Lee
Anthony J
AJ
Gill
Mark S
MS
Sywak
Larry
L
Fingleton
Bruce G
BG
Robinson
Stanley B
SB
Sidhu
Leigh W
LW
Delbridge
D018277:Carcinoma, Mucoepidermoid / Q000473:pathology*; D005260:Female; D006801:Humans; D008297:Male; D008679:Metaplasia / Q000473:pathology; D008875:Middle Aged; D009687:Nuclear Proteins / Q000032:analysis; D013954:Thyroglobulin / Q000032:analysis; D013964:Thyroid Neoplasms / Q000473:pathology*; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors / Q000032:analysis; D055815:Young Adult
C000614412:NKX2-1 protein, human; D009687:Nuclear Proteins; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors; D013954:Thyroglobulin