A case of insular
thyroid carcinoma arising in the right lobe of a 54-year-old male is reported. The tumour exhibited an invasive growth pattern with regional
lymph node metastasis. Microscopically, the tumour was characterised by well-defined solid nests like insulae, including mature follicles containing
colloid and immature follicles without
colloid. Immunohistochemically, tumour cells in follicular areas predominantly exhibited immunopositivity to
antithyroglobulin antibody. On the other hand, diffuse immunoreactions with anti-
neuron-specific enolase (NSE),
S-100 protein and Leu-7 were detected mainly in the tumour cells of solid areas. In addition, clear cytoplasmic immunoreactivity with anti-
myelin basic protein (MBP) antibody was exhibited in a number of tumour cells. Ultrastructurally, many tumour cells possessed dense vacuoles, apparently containing
colloid material, but intracytoplasmic neurosecretory granules were absent. The histopathological and ultrastructural characteristics of the tumour as well as its
anti-thyroglobulin antibody immunoreactivity support the classical hypothesis that this
neoplasm is a variant of poorly differentiated
thyroid carcinoma. The positive immunohistochemical reactions for NSE, S-100, MBP and Leu-7 raise the possibility of aberrant differentiation, for example neural.