Kidney stones (nephrolithiasis) are common, painful mineral deposits that form within the urinary tract. While most stones result from dietary habits and genetic predispositions, cancer or its treatments can directly trigger their formation. This connection involves complex alterations to the body’s chemistry, the physical effects of tumors, and the side effects of aggressive therapies. Understanding these distinct pathways clarifies how malignancy can lead to kidney stone development.
Cancer Types That Alter Systemic Metabolism
Certain malignancies actively alter the body’s internal environment, creating conditions for mineral precipitation in the kidneys. This process often involves the systemic release of substances that disrupt the normal balance of calcium or uric acid in the blood and urine.
A primary pathway involves hypercalcemia (high calcium levels), which predisposes a person to forming calcium-based kidney stones. Some solid tumors, such as squamous cell carcinomas of the lung, head, and neck, produce parathyroid hormone-related protein (PTHrP). This protein mimics the body’s parathyroid hormone, causing calcium to be released from bones into the bloodstream at an uncontrolled rate. Cancers like multiple myeloma and metastatic breast cancer also directly break down bone tissue, releasing large amounts of calcium that the kidneys must excrete, leading to stone formation.
Another metabolic cause is hyperuricemia, an excess of uric acid, which is a breakdown product of cellular material. High-turnover cancers, including acute leukemias and aggressive non-Hodgkin lymphomas, have rapidly dividing cells that release large amounts of purines when they die. When chemotherapy rapidly destroys these cells, a massive release of intracellular contents occurs, known as Tumor Lysis Syndrome (TLS). The resulting spike in uric acid can overwhelm the kidneys, causing uric acid crystals to precipitate and form stones.
Stone Formation Due to Cancer Treatments
The interventions used to fight cancer, while life-saving, can inadvertently create a stone-forming environment. Chemotherapy agents are a common cause, either by increasing the metabolic load or by crystallizing directly in the urine.
Some chemotherapy drugs, including methotrexate, cisplatin, and cyclophosphamide, can contribute to acute hyperuricemia by triggering the rapid death of cancer cells. Even without full-blown Tumor Lysis Syndrome, this increased cellular turnover stresses the kidneys’ ability to manage uric acid excretion. Furthermore, some chemotherapy agents are poorly soluble and may directly precipitate in the renal tubules, leading to drug-specific crystals and stones.
A common side effect of many cancer treatments is severe nausea and vomiting, which leads to significant dehydration. When the body loses fluid, the urine becomes highly concentrated, increasing the saturation of stone-forming minerals like calcium and uric acid. This lack of dilution is a major factor in treatment-related stone development.
Radiation therapy, particularly for pelvic cancers (cervix, prostate, or rectum), can cause stones through physical damage. The radiation can lead to chronic inflammation and scarring in the ureter, the tube connecting the kidney to the bladder. This scarring results in a radiation-induced ureteral stricture, which restricts urine flow. The subsequent stagnation of urine above the blockage (hydronephrosis) creates an environment for stone formation, sometimes leading to complex, infection-related stones.
Direct Obstruction from Kidney Tumors
Beyond systemic effects and treatment side effects, the physical presence of a tumor can directly facilitate stone formation.
Cancers originating in the kidney (e.g., renal cell carcinoma) or those in the collecting system (e.g., transitional cell carcinoma) can mechanically obstruct urine flow. A tumor mass growing within the kidney’s collecting system acts like a physical dam, causing urine to back up and stagnate in the upper urinary tract. This urinary stasis allows minerals to settle out of the solution and aggregate into a stone mass.
Tumors can also contribute to stone formation by causing significant bleeding (hematuria) into the urinary tract. Blood clots that form within the kidney or ureter can serve as a nucleus (nidus) for stone growth. Mineral salts, like calcium, then deposit onto this organic clot, forming a stone physically caused by the tumor’s presence.
Evaluating Stone Composition and Symptoms
When a stone is identified, its composition is valuable diagnostic information, especially for patients with a cancer history or those undergoing treatment. Stones made of pure uric acid or brushite (a form of calcium phosphate) may prompt metabolic investigation for an underlying malignancy or a treatment side effect like Tumor Lysis Syndrome. Conversely, a typical calcium oxalate stone is less likely to be directly related to cancer.
Kidney stones and kidney cancer can present with identical initial symptoms, primarily severe flank pain and blood in the urine. This overlap means that a diagnosis of a stone may occasionally mask an underlying kidney tumor. Communicating any history of malignancy or recent cancer treatment to a urologist is important, as it immediately influences the diagnostic workup. Advanced imaging and chemical analysis of a passed or surgically removed stone are routinely performed to differentiate a common stone from one signaling a systemic problem related to cancer.