Metastasis of breast cancer to the right kidney with a tumor thrombus in the inferior vena cava: a case report

BACKGROUND: It is quite rare for breast cancer to metastasize to the kidney with a tumor thrombus in the inferior vena cava. CASE PRESENTATION: A Japanese woman in her forties was diagnosed with cancer of the left breast and underwent left mastectomy with sentinel lymph node biopsy. The final pathological diagnosis was pT1aN0M0, stage IA (ER positive, PgR positive, HER2 negative). Thirteen years later, she presented for care with the complaint of abdominal pain. By imaging findings, right renal carcinoma with a tumor thrombus in the inferior vena cava and lung metastases was suspected. However, her tumors were refractory to molecular targeted therapy. In addition, CT-guided needle biopsy of the kidney and lung lesions was done and it was revealed that lesions of the left lung and the right kidney was breast cancer metastases (ER positive, PgR positive, HER2 negative). The patient started combination therapy consisting of abemaciclib, tamoxifen and leuprorelin. Six months later, she died from progression of her metastatic disease. CONCLUSIONS: It is sometimes difficult to differentiate between primary renal cancer and kidney metastases from breast cancer on imaging. Renal biopsy is recommended before commencing treatment.