Metastatic Carcinoma to Breast from Renal Cell Carcinoma- A Rare Case Report with Unusual Cytology

Abstract

Metastatic carcinoma to breast is an uncommon entity compared to the primary breast malignancies. Renal Cell Carcinoma (RCC) metastasising to breast is very rare as it commonly metastasises to lung, liver or bone. An accurate diagnosis of Secondary Tumour is must, since the prognosis and treatment differs between primary and secondary tumours. Here, the authors present the case of a 55-year-old female patient who presented with lump in right breast measuring 5×4 cm. Mammographic findings showed relatively well-defined round irregular marginated heterogenous radioopaque mass in outer lower quadrant, Breast Imaging Reporting and Data System (BIRADS- IV B). Fine Needle Aspiration Cytology (FNAC) showed atypical cells arranged in cohesive clusters with focal papillary architecture, entangled in eosinophilic stroma and cellular stromal fragments. The cells were small with ill-defined cell borders, granular to focal vacuolated cytoplasm, mild anisocytosis and indistinct nucleoli. Stain for mucin was negative. The differential diagnosis offered were primary breast carcinoma with possibility of metaplastic carcinoma and metastatic carcinoma. A trucut biopsy showed fibrocellular stroma, islands of cells with clear cytoplasm separated by thin fibrous septa. Immunohistochemical (IHC) for pancytokeratin (panCK), CD10 and vimentin were positive and Estrogen Receptor (ER), Progesterone Receptors (PR), Human epidermal growth factor receptor 2 (HER2) were negative and the diagnosis of metastatic RCC was made. The cytology case reports in the literature have shown characteristic cytomorphological features composed of cells with abundant, finely vacuolated cytoplasm, moderate pleomorphism and prominent nucleoli. This case is unusual as it was predominated by small cells with granular cytoplasm. Therefore, it was concluded that trucut biopsy is mandatory for breast lump in patient with RCC since the cytological features on FNAC might not always be characteristic.