Histology and immunocytochemistry of differentiated thyroid carcinomas do not predict radioiodine uptake: A clinicomorphological study of 62 recurrent or metastatic tumours

Summary

Sixty-two metastases or recurrences of differentiated thyroid carcinomas were investigated using conventional histology and immunocytochemistry for thyroglobulin (TG), thyroxine (T₄) and triiodothyronine (T₃). In each patient,¹³¹I total body scans had been performed 4–10 weeks before surgery. Twenty-seven of the 62 tumours exhibited a predominance of follicles (A₁), while 35 either exclusively or predominantly consisted of papillae or, in the case of follicular carcinomas, were predominantly trabecular or solid in structure (A₂). TG and T₄ immunoreactivity was observed in 60 cases, only 4 of these also expressing T₃. Positive radioiodine uptake (RIU) was noted in 27 of 62 (44%) cases (A₁: 18/ 27=67%; A₂: 9/35=26%), 25 of which showed intraluminal TG and T₄ positivity. Two follicular carcinomas showing RIU lacked follicular lumina, but exhibited strong diffuse cytoplasmic positivity for both TG and T₄. In another 95 differentiated thyroid carcinomas, the structure of primary and secondary lesions was assessed. Of these, 27 (28%) showed a discordant pattern (A₁/A₂ or A₂/A₁) when comparing the structure of primary and secondary lesions. Our data suggest that differentiated thyroid carcinomas show a dissociation of TG/T₄ expression and RIU, defects of iodine uptake and storage being found more frequently than a depression of TG and T₄ synthesis. Intact synthesis of TG and T₄, but not of T₃ may be regarded as a prerequisite for RIU. Positive RIU is based on the presence of mature neoplastic follicles containing TG and T₄ immunoreactive colloid and among follicular carcinomas, positive RIU may be encountered in neoplasms lacking follicular lumina but exhibiting strong cytoplasmic TG and T₄ staining. Finally, the RIU of recurrent and metastatic PC and FC is not predictable from histological features of the primaries.