Mixed epithelial and stromal tumour (MESTK) of the kidney is a rare and benign tumour composed of epithelial and spindle cell stromal components with solid and cystic architecture. MESTK is most commonly seen in perimenopausal women, especially those on long-term oestrogen therapy. MESTK is often asymptomatic, detected incidentally on imaging studies. Diagnosis is established by histological examination. Microscopy is reminiscent of ovarian stroma. Malignant transformation, metastasis and recurrences are extremely rare. Treatment is surgical excision of the tumour with usually no recurrences after surgery and good prognosis. We describe a case of MESTK found incidentally on imaging studies.

Malignant peripheral nerve sheath tumors (MPNSTs) are extremely rare soft tissue sarcomas of ectomesenchymal origin. They are commonly seen in association with neurofibromatosis type 1 (NF-1), but can also occur without a history of NF (isolated MPNST). MPNSTs are most commonly located on the extremities (brachial and sacral plexus), head and neck, and trunk regions and are rarely reported in genitourinary organs. These tumors are aggressive, with a high recurrence rate and distant metastases. MPNST involving the kidney is extremely rare, and review of the literature using PubMed from 2001 to 2014 revealed eight cases of MPNST involving the kidney (seven, primarily involving the kidney and one metastatic MPNST of the kidney). Herein, we describe a case of breast metastases from an MPNST of the kidney without a history of NF-1. The patient was initially diagnosed with a spindle cell neoplasm of the kidney with peripheral nerve sheath differentiation. Eventually, the patient developed a right breast mass that was diagnosed as metastatic MPNST. The patient refused any kind of treatment and died 6 months later in hospice care.