CYTOLOGICAL DIAGNOSIS OF EXTRA THYROIDAL MALIGNANCY IN THYROID-A REPORT OF TWO CASES.

Intra thyroidal metastasis and direct extension of extra thyroidal malignancies can present with clinically palpable nodules and as suspicious nodules on radiological imaging. Metastasis to thyroid is rare and usually discovered during an autopsy especially in individuals with widespread dissemination of the tumor. In autopsy series, the incidence of thyroid metastasis ranges from 0.5% to 24% (1) but is much lower in clinical studies. Most common primary tumors that can metastasize to thyroid include carcinoma of kidney, breast, pancreas, colon, ovary, lung, bladder and malignant melanoma (2). It is rare for these tumors to present initially as isolated thyroid nodule or disturbances in thyroid function and is seen in less than a quarter of cases (3). We reported two cases of extra thyroidal malignancies which were diagnosed by fine needle aspiration cytology. The first case was an invasive breast carcinoma that metastasized to thyroid and another case was direct extension of squamous cell carcinoma of hypopharynx to thyroid. Primary squamous cell carcinoma of the thyroid is rare and its incidence ranges from 0.2-1.1% of all thyroid malignancies (4). Whenever malignant squamous cells are seen admixed with thyroid follicular epithelial cells, the possibility of metastasis from occult primary should always be considered while interpreting thyroid cytology. Squamous cell carcinomas metastasizing to the thyroid largely have their origin in the esophagus, lung and head & neck region. Invasive breast carcinoma is the most common type of breast cancer which constitutes 85% of all invasive carcinomas. Breast carcinoma usually metastasizes to lungs, liver, bones and brain. Solitary thyroid metastasis of invasive breast carcinoma is rare.