Several types of cancer can lower protein levels in your blood, but the most common culprits are liver cancer, blood cancers like multiple myeloma, kidney cancer, and cancers of the digestive tract. Each drives protein levels down through a different mechanism: some cancers destroy the organ that makes protein, others cause your body to lose protein through the kidneys or gut, and still others hijack the cells that produce normal proteins in the first place. Normal blood albumin (the most abundant protein in your blood) falls between 3.5 and 5.0 g/dL in adults, and cancer can push it well below that range.
Liver Cancer
Your liver manufactures albumin, which accounts for roughly 60% of all the protein in your blood plasma. When liver cancer (hepatocellular carcinoma) develops, it usually does so in a liver already damaged by cirrhosis or chronic hepatitis. The combination of existing liver damage and tumor growth severely reduces the organ’s ability to produce albumin. In cirrhotic livers, albumin production drops both because there are fewer functioning liver cells and because the albumin molecules that are made tend to break down faster than normal.
Low albumin in liver cancer patients carries a double meaning. It signals that the liver is failing at one of its core jobs, but research also suggests it reflects how aggressive the cancer is. Studies have shown that when albumin levels fall in liver cancer, markers tied to tumor invasion and spread become more active. In other words, dropping protein levels aren’t just a side effect of liver damage; they may also indicate the cancer is becoming more invasive.
Multiple Myeloma and Related Blood Cancers
Multiple myeloma is a cancer of plasma cells, the immune cells in your bone marrow that normally produce antibodies. In myeloma, these cells multiply uncontrollably and start churning out abnormal protein fragments called light chains instead of functional antibodies. While your total protein count might actually appear elevated on a basic blood test (because of all the abnormal protein), the useful proteins your body depends on, particularly albumin, often drop significantly.
One serious complication is AL amyloidosis, where those excess light chain proteins misfold and clump together into stiff fibers called amyloid fibrils. These fibrils deposit in organs, most commonly the heart and kidneys. When amyloid builds up in the kidneys, it damages the filtering system and allows normal proteins to spill into your urine. You might notice foamy or bubbly urine as an early sign. The result is a steady drain of protein from your bloodstream that your liver can’t keep up with.
Kidney Cancer
Your kidneys act as filters, normally keeping large protein molecules in the blood while letting waste pass into the urine. Kidney cancer (renal cell carcinoma) can disrupt this filtering in several ways. The tumor may directly invade kidney tissue, block blood flow by forming clots in the renal vein, or trigger an immune reaction where the body’s own defenses attack the kidney’s delicate filtration membranes.
This immune-mediated damage is especially notable. The cancer can shed proteins or trigger antibody responses that deposit in the kidney’s filters, making them leaky. The condition that results, nephrotic syndrome, causes massive protein loss through urine. Some patients lose enough protein daily that blood levels drop rapidly, leading to visible swelling in the legs, ankles, and around the eyes. Kidney cancer is well known for producing a wide range of effects beyond the kidney itself, and protein loss through this mechanism is one of the more consequential ones.
Stomach and Intestinal Cancers
Cancers of the digestive tract, including stomach, colon, and small intestine cancers, can cause a condition called protein-losing enteropathy. Normally, the intestinal wall acts as a barrier that keeps blood proteins on the blood side. When a tumor erodes or inflames the intestinal lining, it creates weak spots or outright openings that let proteins leak from the bloodstream into the gut. Once inside the intestines, those proteins travel through the digestive tract and are lost entirely.
This type of protein loss can be difficult to detect early because it doesn’t show up in urine tests the way kidney-related losses do. The first clues are often the physical consequences of low protein: swelling in the legs or abdomen, unexplained weight changes, or persistent fatigue.
How Low Protein Causes Symptoms
Albumin does more than float passively in your blood. It acts like a sponge, pulling fluid from your tissues back into your blood vessels through osmotic pressure. When albumin drops too low, fluid leaks out of your blood vessels and collects where it shouldn’t.
The most noticeable result is edema, or swelling, usually starting in the ankles and legs because gravity pulls the fluid downward. In more advanced cases, fluid accumulates in the abdomen, a condition called ascites. Ascites can cause significant abdominal swelling and bloating, a painful feeling of fullness, clothes that suddenly don’t fit, and shortness of breath as the fluid presses up against the lungs. Appetite loss, nausea, constipation, and fatigue frequently accompany it.
How Doctors Identify the Cause
A basic blood test can tell you that protein levels are low, but it won’t explain why. Doctors use a test called serum protein electrophoresis (SPEP) to separate blood proteins into distinct groups and look at the pattern. This pattern helps distinguish between very different causes. A low albumin band, for example, points toward liver disease, kidney loss, or malnutrition. An abnormal spike in one specific protein group suggests a blood cancer like myeloma. Elevated levels in certain protein fractions can flag active inflammation or malignancy even when total protein looks relatively normal.
From there, the workup depends on what the pattern suggests. Urine tests can reveal whether protein is being lost through the kidneys. Imaging of the liver, kidneys, or digestive tract helps identify tumors. For suspected myeloma, a bone marrow biopsy confirms whether abnormal plasma cells are present. The key point is that low blood protein on its own is a signal, not a diagnosis. It tells your doctor something is wrong, and the pattern of which proteins are low or high narrows down where to look.
Other Cancers That Contribute
Beyond the major categories above, virtually any advanced cancer can lower blood protein levels indirectly. Cancer increases your body’s metabolic demands and triggers chronic inflammation, both of which accelerate protein breakdown. Many people with advanced cancer also eat less due to nausea, pain, or treatment side effects, reducing the raw materials their liver needs to produce albumin. Cancers that spread to the liver, even if they originated elsewhere (like metastatic breast or lung cancer), can impair albumin production by replacing healthy liver tissue with tumor.
Lymphomas deserve a specific mention. Like myeloma, certain lymphomas can trigger kidney damage through immune-mediated processes, leading to protein loss in urine. They can also cause protein-losing enteropathy when they involve the intestinal wall or the lymphatic vessels that drain the gut.
Low blood protein in cancer is rarely caused by a single mechanism. Reduced production, increased loss, and faster breakdown often overlap, especially in advanced disease. Tracking protein levels over time gives doctors useful information about how well the liver is functioning, how the cancer is responding to treatment, and whether nutritional support needs to be adjusted.