Endocrine Abstracts

Introduction: Poorly differentiated thyroid cancer (PDTC) is a rare subtype of thyroid carcinomas, that diagnosis is difficult and often missed in daily routine. It is believed that most of them arise in well-differentiated thyroid carcinoma, although a subset of these lesions apparently also arise de novo.

Case report: In 2007, a 55-year-old man had a total thyroidectomy and received radioactive iodine treatment post-surgery due to well-differentiated papillary thyroid carcinoma (PTC) (pT2N0M0). An endocrinologist examined the patient several times for a possible recurrence of thyroid cancer, but there were no signs: thyroglobulin (TG) was <0.1 μg/l. The patient is currently on thyroxine replacement therapy (targeted thyroid-stimulating hormone <0.1 mIU/l). In 2019, an elevated TG level was detected (6.47 μg/l), and an ultrasound (US) of the neck showed a calcified lymph node in the III zone of the right side. Fine-needle aspiration of the calcified lymph nodes revealed any tumorous alterations and TG did not increase dynamically (4.5 μg/l). In 2020, the patient complained of pain in his left upper arm. A CT scan revealed a pathologic humeral fracture, and a bone tumor biopsy indicated PTC metastasis. CT scan of the neck, chest, abdomen, and pelvis revealed no primary tumor, therefore the right lung root and bronchopulmonary lymph nodes were more likely to be pathological, likewise, a blood test found an elevated TG level (637.5 μg/l). Hence, the humeral tumor was excised, followed by fracture fixation and cementoplasty; the histology of the tumor confirmed PTC metastasis in the bone. The patient was given radioactive iodine therapy in ablating dosages following surgery. Four months after, a CT scan shows slightly enlarged peribronchial and bronchopulmonary lymph nodes, and TG level increased over time up to 716.05 μg/l. After biochemical and radiological progression along with radioactive iodine resistance, the patient’s medical records and cytological features were reviewed – PDTC was diagnosed. Kinase inhibitors have been initiated for cancer treatment (Lenvatinib). In 2022, on a CT scan, the disease has not progressed, and the level of TG has decreased (217 μg/l), indicating that the cancer is likely responding to biological therapy. This year, the patient feels better and has started the 20th cycle of Lenvatinib.

Discussion: PDTC accounts for 2–15% of all thyroid malignancies, consequently, PDTCs, which require a correct diagnosis in order to receive adequate treatment, are often missed in daily routine. In our case, a correct diagnosis was made 13 years after the PTC diagnosis.