Kidney Metastases
Kidney metastases are cancerous lesions that have spread to the kidney from a primary cancer elsewhere in the body. The kidneys have a rich blood supply and can be affected by a wide range of primary cancers, most commonly lung cancer, melanoma, breast cancer, colorectal cancer, and lymphoma, along with others. Kidney metastases are typically identified in patients with a known cancer diagnosis, either during staging or during follow-up imaging, though occasionally they present in patients without a known primary. They are distinct from primary kidney cancers (such as renal cell carcinoma) and require different evaluation and treatment. Management focuses on the underlying primary cancer, with treatment tailored to the specific tumor type and clinical context.
What is it?
The kidneys have a rich blood supply and filter roughly a quarter of the blood pumped by the heart with each beat. This makes them a possible site for the spread of cancer from other parts of the body, though metastases to the kidneys are less common than metastases to other organs such as the lungs, liver, or bones. Kidney metastases refer to cancer cells that have traveled from a primary tumor elsewhere and formed one or more lesions in the kidney. They are distinct from primary kidney cancers—cancers that originate within the kidney itself, such as renal cell carcinoma or transitional cell carcinoma of the renal pelvis—and generally have different appearances on imaging, different treatments, and different implications.
Kidney metastases can arise from a wide range of primary cancers. The most common primary sources include lung cancer (particularly small cell and some non–small cell lung cancers), melanoma, breast cancer, colorectal cancer, and lymphoma. Other primary cancers that can spread to the kidneys include gastric, pancreatic, thyroid, ovarian, testicular, prostate, and various sarcomas. In patients with widespread cancer, kidney metastases may occur as part of disease that has spread to multiple organs (widespread metastatic disease). Less commonly, kidney metastases may be discovered as an isolated site of spread from an otherwise controlled cancer, or in patients without a known primary at the time of discovery.
The clinical significance of kidney metastases depends heavily on the type of primary cancer, the extent of disease elsewhere, the response to treatment, and patient-specific factors. In many cases, the presence of kidney metastases reflects widespread disease and is one of several sites of spread that inform overall treatment planning. Occasionally, an isolated or limited kidney metastasis (as part of “oligometastatic” disease—cancer that has spread to only a few sites) may be considered for local treatment such as surgery, radiation, or ablation, in addition to systemic therapy.
Symptoms of kidney metastases are often absent, particularly when the lesions are small or when the patient’s other cancer-related symptoms dominate the clinical picture. When symptoms occur, they may include flank or back pain (particularly with large lesions or when the collecting system is involved), blood in the urine (which can be more common with lymphomatous involvement or certain aggressive lesions), and symptoms of reduced kidney function in advanced or bilateral disease. Systemic symptoms of cancer (such as weight loss, fatigue, reduced appetite, and, in specific cancers, other symptoms) are often present but reflect the overall disease burden rather than the kidney lesions specifically.
Diagnosis of kidney metastases is usually made through imaging in patients with a known cancer diagnosis. CT with and without contrast is the primary imaging test and can identify the presence, size, number, and location of lesions in the kidneys, as well as evaluate for disease elsewhere. MRI provides similar information without ionizing radiation and can be particularly useful in patients who cannot receive iodinated contrast. Ultrasound may identify larger lesions but is less useful for detailed characterization. PET/CT is used in the evaluation and staging of many cancers and can identify kidney metastases in the context of the broader disease pattern. For lymphoma, dedicated evaluation with PET/CT and, when needed, biopsy is often central to management.
Imaging features that suggest metastases (rather than a primary kidney cancer) may include multiple lesions in one or both kidneys, small to moderate size, characteristic appearance in the context of a known primary cancer, and the presence of disease elsewhere. However, imaging alone cannot always distinguish metastases from primary kidney cancer, and in selected patients—particularly when the diagnosis would significantly change treatment—image-guided biopsy of a kidney lesion may be performed to confirm the diagnosis and characterize the tumor.
Blood tests including kidney function (creatinine and eGFR) are important, as they influence treatment options. Additional tests depend on the primary cancer and the overall clinical context.
For patients without a known primary cancer at the time a kidney lesion is discovered, the imaging features may suggest whether the lesion is more likely a primary kidney cancer or a metastasis, and evaluation may include a broader workup for possible primary sources. This can include CT of the chest, abdomen, and pelvis, PET/CT, other imaging as appropriate, laboratory testing, and, when needed, biopsy of the kidney lesion or of another lesion (such as a lymph node) to obtain a pathologic diagnosis. Modern molecular and immunohistochemical testing of biopsy specimens can often help identify the likely primary source when it is not already known.
Important to Know
Management of kidney metastases is directed by the type of primary cancer, the extent of disease, the patient’s overall health and preferences, and, when relevant, the specific molecular characteristics of the tumor. Care is best coordinated by multidisciplinary oncology teams that include medical oncologists, radiation oncologists, urologic oncologists (when local kidney treatment is being considered), radiologists, pathologists, and palliative care specialists, along with primary care and other clinicians as needed.
Systemic therapy is usually the mainstay of treatment for cancer that has spread to distant organs, including the kidneys. The specific treatment depends on the primary cancer type. Examples include chemotherapy (used for many cancers), immune checkpoint inhibitors (increasingly important in melanoma, lung cancer, and many other cancers), targeted therapies matched to specific molecular alterations (such as EGFR-, ALK-, or ROS1-directed therapies in lung cancer, HER2-directed therapies in breast cancer, BRAF-directed therapies in melanoma, and many others), hormonal therapies (in hormone-sensitive breast, prostate, and other cancers), and chemoimmunotherapy regimens (in lymphoma). The specific choice of therapy is highly individualized and follows established treatment principles for the specific cancer.
Local treatment of an isolated or limited kidney metastasis may be considered in selected patients, particularly in the setting of oligometastatic disease (cancer with limited sites of spread) and when the primary cancer is otherwise well controlled. Options include surgical removal (typically partial nephrectomy when feasible, or radical nephrectomy in selected cases), stereotactic body radiation therapy (SBRT, which delivers highly focused radiation in one or a few sessions), and thermal ablation techniques (such as radiofrequency ablation or cryoablation). The decision to pursue local treatment is highly individualized and typically made by a multidisciplinary team.
For patients with lymphoma involving the kidneys, treatment follows lymphoma-specific principles based on the lymphoma type and stage. This often includes chemoimmunotherapy (such as regimens containing rituximab for B-cell lymphomas), radiation in selected cases, and other approaches. Kidney lymphoma is often responsive to appropriate treatment, and initial evaluation of new kidney lesions in patients with lymphoma should consider this possibility.
For patients with cancer of unknown primary presenting with a kidney lesion, evaluation and treatment are guided by the pathology, molecular characteristics, and any additional findings identified during the workup.
Care of kidney function is an important consideration throughout treatment. Some cancer therapies can affect kidney function, and the presence of kidney metastases can also affect function, particularly when both kidneys are involved or when the collecting system is obstructed. Careful attention to hydration, avoidance of medications that can harm the kidneys (when possible), management of related conditions such as high blood pressure and diabetes, and coordination with nephrology when needed all support kidney health.
Symptom management and palliative care play an essential role throughout the treatment journey, regardless of the specific cancer type. Palliative care can be integrated alongside cancer-directed therapy at any stage and is particularly valuable in managing pain, other symptoms, and quality of life. It is not limited to end-of-life care.
Nutritional support, mental health support, physical activity as tolerated, and support for family and caregivers are important components of comprehensive cancer care.
Follow-up during and after treatment includes periodic imaging (to assess response and monitor for progression), laboratory testing, clinical assessment, and, when appropriate, tumor markers. Surveillance schedules are individualized based on the primary cancer, treatment response, and clinical context.
Care during pregnancy in patients with metastatic cancer requires special attention. Some treatments have implications for the fetus, and coordination with obstetrics, maternal-fetal medicine, and oncology is essential. Fertility considerations may be important for patients of reproductive age receiving treatment.
Care is best coordinated by multidisciplinary oncology teams. Imaging, laboratory, pathology, and molecular findings are interpreted alongside the patient’s symptoms, examination, treatment history, and broader clinical context rather than in isolation.
Patient education plays an essential role. Understanding the diagnosis, the specific characteristics of the primary cancer, the rationale for the recommended treatment plan, the meaning of imaging and laboratory findings, treatment side effects, and warning signs of complications all contribute to better outcomes. Clear communication and shared decision-making between the patient, family, and healthcare team are central.
Red flag symptoms include severe flank or back pain, high fever with signs of severe infection or possible kidney infection (chills, back pain, and nausea), significant decrease in urine output, significant blood in the urine (including clots), severe abdominal pain, sudden severe symptoms of hypercalcemia (severe weakness, confusion, dehydration, which can occur in some cancers), severe symptoms of tumor lysis syndrome after starting treatment (electrolyte disturbances, kidney failure), new severe back pain with weakness, numbness, or bowel or bladder changes (which may indicate spinal cord compression), or rapid clinical deterioration. These warrant prompt or urgent medical evaluation.