Role of cytology in differentiating anaplastic thyroid carcinoma with osteoclast like giant cells from giant cell variant of medullary thyroid carcinoma

Anaplastic thyroid carcinoma (ATC) is a highly aggressive tumor and constitutes 2%–5% of all thyroid carcinomas. The cytological diagnosis of osteoclast giant cell variant of ATC is extremely rare, and only a few cases have been described in literature. A 67 - year-old female underwent fine-needle aspiration cytology from the thyroid nodule. Smears revealed hypercellular aspirate comprising of clusters and singly scattered atypical cells with few interspersed multinucleated tumor cells. Cytomorphological differential diagnosis of giant cell/pleomorphic variant of medullary carcinoma and anaplastic carcinoma was offered. Histomorphological features on cell block assisted with immunohistochemistry confirmed the diagnosis of ATC with osteoclastic-like giant cells. Computed tomography-guided right lung lesion aspirate was reported as metastasis of high-grade poorly differentiated carcinoma. The patient was managed with cisplatin-based chemotherapy. This case highlights the importance of cytological diagnosis of ATC to guide the treatment modality of chemotherapy thus avoiding surgery, especially in old moribund patient with lung metastasis.