CASE REPORT OF RENAL CELL CARCINOMA TO THE BREAST

Objectives: Breast cancer is very common in women, however, metastases to the breast are extremely rare with an incidence up to 2% reported in literature. Melanoma, lymphoma, and leukemia are the cancers most likely to metastasize to the breast. Renal cell carcinoma (RCC) usually metastasizes to the lung, bone, lymph nodes, liver, and brain. However, it is also known to form micrometastases in unusual organs such as the thyroid or pancreas. This report describes a renal cell carcinoma breast metastasis that was treated with surgery.

A 68-year-old female with a history of left renal cell carcinoma treated with left nephrectomy 20 years prior presented to clinic with a new abnormality on a screening mammogram. She had no palpable masses in her breast, but diagnostic mammogram confirmed a subtle architectural distortion in her right upper outer breast. Ultrasound reveal a 0.6 x 0.6 x 0.5 cm irregularly shaped mass with posterior shadowing. Biopsy was performed and returned as a pigmented carcinoma, at least ductal carcinoma in situ. However, after review by several pathologists, it was confirmed to be metastatic renal cell carcinoma involving breast tissue. The tumor was positive for renal markers racemase and PAX8, and negative for breast marker GATA3 and estrogen receptor. Workup was negative for further metastatic disease, so she underwent a partial mastectomy with needle localization. On pathology, no residual tumor was identified at the site of the biopsy, and only fibrocystic changes were seen. When discussed at an institutional tumor board, the team recommended monitoring with PET scans and to forego chemotherapy and radiation therapy at this time given the small size of the lesion.

Renal cell carcinoma is an uncommon cancer, and there have been less than 50 cases of breast metastases reported in literature. These metastases are often not treated with surgery, as there is usually widespread metastatic disease. A combination of chemotherapy and immunotherapy, such as protein-tyrosine kinase inhibitors and anti-PD-1 monoclonal antibodies, is often used. Breast metastases have been found months to years after nephrectomy, so it could be beneficial to stain for RCC in biopsies of patients with a new breast mass and history of renal cell carcinoma. In the setting of an isolated breast metastasis, it appears to be beneficial to treat with surgery alone.

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