RESUMO
Primary breast lymphoma is a relatively uncommon neoplasm, majority being of B-cell origin. Mucosa associated lymphoid tissue (MALT) is one of the common types of breast lymphomas. Though cytologic diagnosis of breast lymphoma is an easy procedure and provides guidance for appropriate pre-operative management, it is often impossible to differentiate a low grade lymphoma from reactive proliferation. A similar difficulty was encountered in the present case, a 42 year old female with a breast lump. Fine needle aspiration cytology revealed a mixed lymphoid cell population. Lymphoepithelial lesions were identified histologically, and the majority of the cell population were confirmed as lymphoma cells of B-cell origin on immunohistochemistry. This case highlights the limitations of cytology and the importance of histological examination supported by immunohistochemistry for making a diagnosis of low grade primary breast lymphoma.