The immune system is designed to act as your body’s natural defense force, identifying and destroying threats like viruses, bacteria, and damaged cells. However, when problems happen within this system, two major health conditions can arise: autoimmune diseases and cancer.
While these conditions affect the body in very different ways, scientists have uncovered a complex, two-way relationship between them. In this article, we explain what autoimmune diseases are, why each condition occurs, how they differ, and how they can happen at the same time.
What is an autoimmune disease?
An autoimmune disease occurs when the immune system accidentally loses its ability to tell the difference between your own healthy tissues and foreign invaders. This is usually due to a combination of genetics and environmental triggers. Instead of protecting the body, the immune system turns against healthy organs, joints, or tissues. It launches these attacks in two main ways:
Sending specialized white blood cells (T cells) to directly destroy the tissues.
Creating abnormal proteins called autoantibodies that mistakenly target the body’s own cells.
Is cancer an autoimmune disease?
No. Cancer is not an autoimmune disease. But both autoimmune diseases and cancer involve the immune system.
In autoimmune conditions, the immune system works overtime. In cancer, the immune system is not working as well as it should.
Why do autoimmune diseases and cancer occur?
Although both conditions involve the immune system, their root causes and behaviors are fundamentally different.
Why autoimmune diseases occur
Autoimmunity happens when the immune system loses its natural "tolerance." This refers to the built-in controls that normally stop the immune system from attacking the body's own cells. Triggers such as genetic susceptibility, viral infections, or environmental exposures (like smoking or chemical exposure) can break down these protective safeguards. As a result, the immune system loses its ability to tell healthy tissue from foreign invaders . This leads to long-term inflammation and tissue damage.
Why cancer occurs
Cancer develops when normal cells undergo genetic mutations that cause them to divide and multiply uncontrollably, forming tumors. In contrast to autoimmune diseases, where the immune system mistakenly attacks healthy cells, cancer often thrives because the immune system fails to attack dangerous ones. Tumor cells can evade detection or actively trick the immune system into ignoring them as a threat.
Common autoimmune diseases
According to a recent Mayo Clinic study, 4.6% to 8% of the U.S. population is estimated to live with one or more autoimmune diseases. Among the most common are:
Rheumatoid arthritis: Causes chronic inflammation and pain in the joints.
Systemic lupus erythematosus (SLE): Affects multiple organ systems, including the skin, joints, kidneys, and blood cells.
Systemic sclerosis: Also called scleroderma, causes thickening and hardening of the skin and internal connective tissues.
Idiopathic inflammatory myopathies (myositis): Causes muscle weakness and inflammation.
Sjögren’s syndrome: Primarily affects moisture-producing glands, leading to dry eyes and dry mouth. This is different from some side effects from chemotherapy that may cause dry eyes or mouth.
What makes autoimmune diseases and cancer different?
The core difference lies in how the immune system behaves:
Feature | Autoimmune diseases | Cancer |
Immune activity | An overactive immune system that affects healthy tissue. | The immune system is weakened and cannot identify or destroy abnormal cells. |
Cell growth | Driven by ongoing inflammation and tissue destruction. | Driven by rapid, uncontrolled cell division and tumor formation. |
What it affects | The body's own healthy organs, joints, or tissues. | The abnormal cancer cells that spread locally or systemically and use nutrients that other healthy cells need. |
Main treatment goal | Calming or suppressing the immune system to reduce inflammation. | Removing the cancer or stopping cancer cell growth with surgery, radiation, or systemic therapy. Immunotherapy and targeted therapy can help activate the immune system to help with this goal. |
Is it possible to have an autoimmune disease and cancer at the same time?
Having an autoimmune disease does not mean a person will automatically develop cancer, but research shows clear overlaps between the two conditions. There are four main scenarios where autoimmune diseases and cancer occur together: if the body is under inflammation during long periods of time, if the cancer itself triggers an immune response, some treatments for autoimmune diseases can increase the risk of cancer, and some cancer immunotherapies can trigger an autoimmune response.
Chronic inflammation: When an autoimmune disease causes ongoing, long-term inflammation and tissue damage, damaged cells must constantly repair themselves. Over time, this rapid cell turnover increases the chances of genetic errors that can lead to cancer. For example, people with Sjögren’s syndrome have a significantly higher risk of developing non-Hodgkin lymphoma (especially MALT lymphoma) due to chronic immune activation in lymphoid tissue.
A cancer develops first and triggers an autoimmune disease. When cancer cells mutate, they produce altered proteins. As the immune system fights the tumor, it creates antibodies against these mutated proteins. If these cancer proteins resemble healthy body tissue, the antibodies cross-react and affect healthy organs. For example, in people diagnosed with scleroderma (with anti-RNA polymerase III antibodies), a cancer diagnosis often occurs within 3 years of the autoimmune diagnosis. Treating the underlying tumor can lead to dramatic improvement in the autoimmune symptoms.
Treatment for autoimmune diseases that may increase cancer risk, this is because these medications are designed to suppress the immune system, making it harder for the body to identify precancerous cells or viral infections. For example, medications like cyclophosphamide (often used for severe vasculitis or lupus) can increase the risk of bladder cancer and blood malignancies like myelodysplastic syndromes (MDS) at higher cumulative doses.
Cancer immunotherapy treatments may cause autoimmune-like side effects. Cancer treatments like immune checkpoint inhibitors (ICIs), work by increasing the immune system activity to eliminate cancer cells. However, removing this may cause side effects called immune-related adverse events. These side effects can imitate classic autoimmune conditions, causing inflammatory arthritis, dry eyes and mouth, and muscle soreness.
People with pre-existing autoimmune diseases who undergo checkpoint inhibitor therapy may experience a flare-up of their underlying condition.
Whether an autoimmune disease arises from chronic inflammation, a tumor triggers an immune response, or cancer treatments activate immune pathways, understanding these connections helps create a more personalized treatment. By combining cancer screening with careful monitoring of immune health, patients and their care teams can navigate both conditions safely.
Keep track of your health with your Personal Health Record
Managing an autoimmune condition, a cancer diagnosis, or both means tracking multiple specialists, lab results, imaging reports, and medication histories. Keeping everything organized is vital for getting the best care possible.
You can securely connect your records, explore personalized treatment options, complete patient surveys and with your permission, share anonymized medical data to help researchers accelerate scientific discoveries.
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