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

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.