An unusual tumour of the breast: cytological findings

The epithelioid variant of malignant peripheral nerve sheath tumour (MPNST), or epithelioid malignant schwannoma is an unusual form of MPNST that closely resembles carcinoma or melanoma as the tumour is composed predominantly of Schwann cells with a polygonal epithelioid appearance. It has been estimated that 5% or fewer MPNST belong to this group. The tumours follow a distribution similar to that of the ordinary MPNST, mostly occurring in patients 20–50 years of age, and may arise in the deep and superficial soft tissues of almost every anatomical site, with rapid growth and aggressive biological behaviour. Most of the tumours reported in the literature originated in major nerves. It is the cases in which the origin from a nerve cannot be documented that pose the most challenging problems in diagnosis. MPNST are some of the most difficult soft tissue tumours to diagnose by fine needle aspiration (FNA) and the results vary greatly depending upon a number of factors including the experience and skill of the aspirator and interpreting cytopathologist. The first description of the cytomorphological features was in 1989 by Molenaar et al. The majority of the cases described in the literature are isolated reports. Difficulties in the FNA diagnosis of schwannoma have been reported by many authors, especially of epithelioid malignant schwannoma. The aim of this paper is to present our case of FNA of epithelioid malignant peripheral sheath tumour of the breast with special reference to the cytological findings. Case report