Case of the Month – July 2019

By Dr Kerry McMahon


40 year old Pacific Islander woman presents with history of lump in right breast.


Bilateral Breast ultrasound performed.


Large predominately solid mass in right breast with vascularity and cystic component superiorly.

Differential diagnosis

  1. Phyllodes tumour – generally present in middle age women as rapidly growing mass with cystic cleft like spaces – reflecting the histologic findings taken from the Greek word “phyllodes” referring to leaf like structures. The microscopic features show cleft like areas with frond type growth and hence the name.
  2. Primary breast cancer
  3. Giant fibroadenoma
  4. Mesenchymal tumour


Biopsy and surgical review

Histology results: provisional

The cores of breast tissue are entirely replaced by a poorly differentiated malignancy. There are sheets of highly pleomorphic, malignant epithelioid cells with very high nuclear to cytoplasmic ratios. Zones of tumour necrosis are present. Some features suggest neuroendocrine differentiation.

Pathology summary

Pathology results demonstrated that this was an undifferentiated small blue cell tumour with immunohistochemical features in keeping with a primitive neuroectodermal tumour of the Ewing sarcoma family. All epithelial, myogenic, melanocytic and lymphoid markers were negative. Further sub classification required PET FISH cytogenetic studies, as this family of tumours can harbour specific cytogenetic rearrangements and came back POSITIVE for EWSR1/FLI1 fustion, which is associated with Ewing sarcoma.

Final summary and treatment

Primitive neuroectodermal tumour with immunohistochemical and cytogenetic features of Ewing sarcoma. Treatment will be a combination of systemic chemotherapy, surgery and radiotherapy.

Case comment

This is a very rare case. Sarcomas of the breast represent <1% of breast malignancies. The most common presentation of a rapidly growing mass in the breast with the above features would be a Phyllodes tumour, which are often benign, though can have borderline and malignant presentations. Ewing sarcoma more commonly present as aggressive bone/soft tissue tumours in adolescent children and young adults.

It is exceedingly rare to present in the breast, with only limited case reports in the literature. Advances however in pathology techniques have led to an increase in pre-operative diagnosis. This group of tumours is characterised by the presence of the typical translocation t (11; 22) (q24; q12), the EWS-FLI1 chimere transcript at the molecular biology and the expression of CD99 antigen (MIC2) at immunohistochemistry.

COM Jul2019