Abstract :
Immunohistochemistry (IHC) is an indispensable complement in anatomy-pathology. It can only be interpreted according to clinical and morphological diagnostic orientations. We report a case of bone metastasis of primary pulmonary papillary carcinoma initially considered thyroid and we will emphasize the interest of immunostaining by thyroglobulin (Tg) and Thyroid Transcription Factor 1 (TTF1). Our case is about a 47-year-old patient who was admitted to the service for bone metastases likely of thyroid origin. The anatomy-pathological study of the surigical specimen initially based on the standard morphological study was back in favour of papillary thyroid carcinoma (PTC). The cervical ultrasound had objectified a normal thyroid volume and a hypoechogenic range of 4 mm. Thyroid status was normal with TSH at 1.8 µUI/ml and non-high Tg at 9ng/ml. A second reading of the surigical specimen with immunohistochemical complement was requested returning in favor of a moderately differentiated papillary carcinoma whose immunohistochemical profile: anti Tg negative, anti TTF positive and anti cytokeratine 7 (CK7) positive, oriented towards a lung origin. An extension assessment made of a chest-abdominal-pelvic computed tomography (CT) scan had objected a right basal parenchymal condensation associated with underlying pleural thickening. A CT-guided lung biopsy was performed and the anatomy- pathological study supplemented by immunohistochemistry returned in favor of a pulmonary papillary adenocarcinoma (PPA) primitive with: anti Tg negative and anti TTF1: intense and diffuse positive marking of tumor cells. The Anatomy-pathology supplemented by immunostaining by Tg and TTF1 allows the diagnosis of certainty of papillary thyroid carcinoma.
