We report a case of a 36-year-old lady who presented with a huge fungating tumour that involved the entire right breast. The tumour was diagnosed histologically as undifferentiated primary stromal tumour of the breast with axillary lymph node metastasis. We review the literature of this rare malignant tumour. Stromal sarcomas of the breast lack epithelial participation, and diagnosis of these tumours can be difficult. Genome-wide expression profiling is currently used to determine the cell of origin of most sarcomas. Surgery offers the best therapeutic option. Adjuvant radiotherapy is not very beneficial, while chemotherapy has, to date, no established role in the management of this disease. The prognosis is dismal for patients with lymph node involvement. The size of the tumour has a lesser bearing on outcome.