Renal Cell Carcinoma Metastasis to the Breast: A Rare Presen
A 73-year-old woman presented with persistent mid and lower abdominal pain. She is known to have IBS, and blood investigations showed iron deficiency anemia. At the time of presentation, the patient had no relevant history of medical comorbidities nor history of smoking; National Early Warning Score (NEWS) was 1. She was referred for abdominopelvic ultrasonography which revealed left renal mass around 18 cm with a mixed solid and cystic component; also, hypoechoic foci were noted within the pancreas.

Subsequent chest CT and CT urogram were done and confirmed a large left renal mass of 18cm × 10cm × 12cm with central necrosis and peripheral hypervascularity. The left renal vein was patent. The adrenal gland looked separable from the mass. Multiple hypervascular foci were noted within the pancreas. Small lung nodules were also noted. The multidisciplinary team (MDT) decision was for cytoreductive nephrectomy and to consider systemic therapy. A month later, the patient had an open left nephrectomy. Renal cell carcinoma, clear cell type grade II, with no lymphovascular invasion, was evident in pathological assessment; surgical margins were clear; and the tumor was classified as grade II pT3a clear cell renal cancer with evident renal vein involvement and no involvement of Gerota's fascia, adrenal gland, perinephric fat, or adjacent organs.

She had evidence of a small volume of metastatic disease in her preoperative imaging. Follow-up every 3 months was scheduled; interval scans in between guided by the clinical examination were done. Initially, the patient had shown stable minimal progress of the metastatic disease for which systemic therapy was not indicated at that time. 16-month post nephrectomy, CT follow-up revealed stable chest disease with new hepatic metastasis for which she started sunitinib treatment. Three months later, brain CT showed brain metastasis after she got an episode of confusion. So full head radiotherapy was started. Further progression of the metastatic disease and recurrence of the primary with new deposits in the spine was noted for which radiotherapy was indicated. At the same time, the patient was referred to the red flag breast clinic for assessment of a newly felt lump in her right breast. On examination, the lump was in the upper part of the right breast 1-2 cm, hard, and poorly mobile with no signs of fixation to the covering skin or the underlying muscle. There was fullness in the axillae but no discrete palpable nodes. The patient stated that she had a positive family history of breast cancer.

Bilateral mammography showed a dense new mass lesion as compared to her previous mammogram done 2 years earlier. The mass was seen in the upper half of the right breast without microcalcifications. Since it was a new finding, an M4 score was given. Breast ultrasound (US) confirmed a rather well-defined hypoechoic solid mass lesion in the right breast at 1 o'clock measuring 20mm × 13 mm with tiny cystic changes. Axilla was normal. It was reported as U5 in ultrasound. US-guided core biopsy was done in the same clinic. Even though the patient had widespread RCC metastatic disease, it was important to clarify if this lesion represented a primary breast tumor which should indicate endocrine therapy (if ER-positive) or a secondary from the RCC which should be managed conservatively unless getting symptomatic.

Pathology revealed breast tissue infiltrated by tumor with a nested pattern composed of clear cells. A panel of immunohistochemical markers reveals positive staining with the renal markers PAX 8 and carbonic anhydrase. CK7 is negative as are the breast markers GATA 3 and mammaglobin. Given the clinical history, the features were those of metastatic renal cell carcinoma.