A case of matrix-producing metaplastic carcinoma of the breast exhibiting similarities to pleomorphic adenoma on fine-needle aspiration cytology

The distinction between matrix-producing metaplastic carcinoma (MPMC) and pleomorphic adenoma (PA) is sometimes unclear in breast pathology, especially on core needle biopsy. Herein, we presented a 66-year-old woman with MPMC of the breast that looked like PA on fine-needle aspiration cytology (FNAC). On FNAC, the appearance of abundant myxoid matrix along with cellular clusters composed of monotonous cellular populations looked like salivary PA, which we were familiar with owing to the frequency in routine pathological practice. Thus, the possibility of breast PA, the counterpart of salivary PA, was considered. However, the tumor location was different from where breast PA frequently occurs, i.e. the retroareolar region. Therefore, we eliminated the possibility of breast PA and avoided the erroneous cytological diagnosis. It is should be kept in mind that MPMC can look like PA on FNAC.