Proteinuria as a Symptom of Cancer
In some cases, proteinuria may be caused by cancer already present within the body. Tumors that invade the kidneys can lead to proteinuria. Whether the cancer originates in the kidneys or spreads there from another location, tumors can cause damage or swelling in the kidneys. They may also cause blood clots in the renal vein. Damage to the kidneys often causes them to malfunction and allows protein to escape into the urine .
Urothelial carcinoma, cancer of the urothelial cells that line the bladder, urethra, ureters, and renal pelvis, can lead to elevated urine protein. It's believed that the urothelial carcinoma may leak protein into the urine .
Multiple myeloma, a cancer that attacks the plasma cells of the blood, can cause the body to secrete Bence-Jones protein in the urine. Bence-Jones protein can damage the kidneys, but unlike other proteins, they don't show up in urine test strips. Your doctor must order a lab urine test to detect this type of urine protein .
With certain types of lung cancer, the first manifestation in the body can be nephrotic syndrome with accompanying protein in the urine. Although this is rare and the reasons it occurs aren't well understood, it's important to be aware of the possibility that nephrotic syndrome could be the first presenting symptom of lung cancer .
Proteinuria as a Predictor of Mortality
The relationship between proteinuria and cancer isn't entirely understood, and the research is ongoing. However, it's clear that elevated urine protein is associated with a higher incidence of cancer and a higher risk of mortality. Multiple studies across different populations have demonstrated that even trace amounts of protein in the urine are related to an increased risk of death from cancer. Generally, the more protein in the urine, the greater the risk of death , , .
One study researching the association between nephrotic syndrome and cancer found a 73% increased risk of cancer in patients with nephrotic syndrome in the five-year follow-up period following diagnosis. The site-specific cancers most prevalent in these patients were lung cancer, kidney cancer, lymphoma, and multiple myeloma. The patients with nephrotic syndrome also had a higher mortality rate than those without . Another study found that the median survival time of cancer patients with accompanying proteinuria was only half as long as that of patients without protein in their urine .
Other Cancer Symptoms
Proteinuria is one potential sign of cancer. Although symptoms can vary between people and depending on the type of cancer, some general symptoms frequently occur in cancer patients. These include
- Unexplained weight change
- Lack of appetite or trouble swallowing
- Nausea or vomiting
- Swelling or lumps
- Unusual bleeding or bruising
- Bladder or bowel changes
- Fever or night sweats
- Vision or hearing changes 
If you have one or more of these symptoms, talk to your doctor. You can also use a urine test strip to check for protein, as this will give you more information to pass on to your healthcare provider.
What if You Have a Positive Urine Protein Test?
Urinalysis test strips can help you monitor your health and catch problems early on. If a urine test strip shows protein in your urine, don't panic. Cancer is only one of many potential causes of kidney disease and proteinuria. However, it's critical to follow up with your healthcare provider. Even if the protein in urine isn't related to cancer, kidney disease is a significant health concern that needs treatment and follow-up. If it is related to cancer, prompt treatment is essential for the best prognosis.
Your doctor is likely to order further testing to help pinpoint the cause of the proteinuria and determine if cancer is present. They might request a 24-hour urine protein test or a urinalysis conducted by a lab. These urinalyses help your doctor better understand the amount and type of protein in the urine, giving them further insight into its cause. They might do a kidney biopsy, where they take a small sample of tissue from your kidney to test it for damage. They might also order bloodwork or imaging tests. Complete all follow-up testing to ensure an early and accurate diagnosis.