A rare case of tumor-to-tumor metastasis: breast cancer metastatic to a benign renal mass
A 67-year-old Caucasian female presented for evaluation of a right chest wall mass 19 years after a modified radical mastectomy for a Stage IIB hormone-receptor positive invasive ductal carcinoma. She received adjuvant chemotherapy and endocrine therapy and had been symptom free until presentation.\nA PET-CT was performed, which demonstrated a round enhancing 1.8 × 1.5 cm right subpectoral lymph node with FDG uptake and a maximum SUV of 4.0 suspicious for metastatic disease (Figs and ). Additionally, an incidental 4.1 × 3.4 cm mass within the midpole of the left kidney was heterogeneously enhancing with increased FDG uptake and a maximum SUV of 8.6 suspicious for a renal cell carcinoma or less likely a transitional cell carcinoma (Figs and ).\nAn ultrasound guided core biopsy of the subpectoral lymph node verified metastatic carcinoma of breast origin, confirmed by positive immunostaining for mammaglobulin, e-cadherin and estrogen receptors (Fig. ).\nWith the relatively small burden of metastatic breast disease, surgical management for the renal mass was deemed appropriate and she underwent a left total nephrectomy without complications.\nThe kidney measured 10.5 × 7.5 × 5.5 cm and was distorted by a 6.0 × 5.5 × 4.0 cm tan-brown mass with a pseudocapsule at the inferior pole (Fig. ). Within the tan-brown mass was a centrally located 2.0 × 1.5 cm white mass (Fig. ).\nThe final pathology demonstrated a 2 cm metastatic mammary carcinoma within a 6 cm angiomyolipoma, confirmed by staining with melan A. All the margins were clear and the renal parenchyma was uninvolved. The metastatic focus was composed of cytologically atypical glands with intraluminal blue mucin, morphologically similar to the subpectoral lymph node biopsy. The metastatic cells also stained positive for the estrogen receptor, mammaglobulin and GCDFP-15, confirming the tumor to be of breast origin (Fig. ).\nThe patient did well post-operatively and was discharged home in a timely fashion after her nephrectomy. At her 7 month follow-up, she continues to take anti-estrogen hormonal therapy and has no demonstrable progression of disease. She has been offered surgical excision of the subpectoral lymph node, but declines at this time.