Endocrine Abstracts

Introduction: Most differentiated thyroid cancers (DTC) have a good response to treatment. However, about 5% of DTC exhibit resistance to radioiodine (RAI), thus having a poor prognosis. Resistance to RAI occurs as a result of losing thyroid differentiation. Immunohistochemical analysis of thyroid cancers shows a substantial ability to predict cancer recurrence and its resistance to RAI.

Case reports: The first case is a of a 66-year-old female, known with total thyroidectomy and bilateral laterocervical lymphodissection for papillary thyroid carcinoma. At the last assessment, whole body scintigraphy showed lung metastasis and an iodine fixing area in the right paratracheal region for which 140 mCi RAI was administered. Tissue section from the lateral and lower tracheal tumor block was subjected to immunostaining (TTF1, PAX8, Thyroglobulin, CK19 were positive in tumor cells, Ki67 15%) which confirmed the local secondary determination of poorly differentiated carcinoma originating in papillary carcinoma with clear and tall cells with weak affinity for capturing RAI. The second case is of a 77-year-old female, known with poorly DTC with trabecular pattern and outstanding areas of sclerohyalising type, with areas of capsular angioinvasion. Immunohistochemical markers (TTF1, PAX8 and Thyroglobulin positivity over 80%, Ki67 3%) indicated the possibility of response to radiotherapy, but with high risk of distant metastases. The third case is of a 45-year-old female, known with total thyroidectomy for poorly DTC and pulmonary and supradiaphragmatic lymph node metastases. Increased value of thyroglobulin (5141 ng/ml, N:3.5-77), the cumulative dose of 240 mCi RAI, the lack of iodine capturing images on anterior cervical region and whole body scintigraphy, as well as positive immunohistochemical markers (TTf1, PAX8, Thyroglobulin, CK19, Ki67 25%) for poorly DTC may suggest a decrease in the chances of response to future radiotherapy.

Conclusion: The case series highlights the predictive capabilities of the immunohistochemical analysis concerning the dedifferentiation of thyroid cancers and their resistance to RAI.