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Case of the Month



Metastatic Breast Carcinoma

A 29-year-old woman with a family history of functional thyroid disorder is seen by her PCP for routine physical examination. The physician notices a right lower pole thyroid nodule and orders blood work and an ultrasound. Blood work shows a normal TSH, FT4, and FT3. The ultrasound describes a single, 1.8 cm nodule iin the right lower pole. The nodule has sharp circumscription and increased vascularity. There are no calcifications. An FNA biopsy of the nodule is recommended. The aspirate smears are markedly cellular and demonstrate a homogeneous population of malignant single cells and cohesive clusters. The clusters are disorderly consisting of irregularly arranged, crowded cells. The nuclei show coarse chromatin, prominent nucleoli, single cell necrosis, and mitotic figures. Occasional intracytoplasmic lumina are present.

Immunoperoxidase stains, performed on a formalin fixed paraffin embedded cell block, show that the neoplastic cells are positive for mammaglobin and negative for thyroglobulin and TTF-1. The thyroid nodule was diagnosed as metastatic adenocarcinoma consistent with a breast primary. Follow-up mammogram demonstrated a right breast mass. Core biopsy of the breast mass showed invasive high grade ductal carcinoma that was cytomorphologically similar to the thyroid lesion.