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Cancer
Research suggests an overall correlation between autoimmune diseases and cancer, in that having an autoimmune disease increases the risk or likelihood of developing certain cancers. Autoimmune diseases cause inflammation through a variety of mechanisms, however, the way in which inflammation is created does not greatly influence cancer risk. Rather, the cancer risk is largely dependent on the fact that all autoimmune diseases increase chronic inflammation which has been linked to cancer. Below are some autoimmune diseases most commonly linked to cancer including celiac disease, inflammatory bowel disease (Crohn's disease and ulcerative colitis), multiple sclerosis, rheumatoid arthritis, and systemic lupus erythematosus, as well as the prevalence of their associated cancers.

The numbers corresponding to the cancer represent the standardized incidence ratio (SIR) unless otherwise noted. The SIR should be interpreted as the incidence of cancer in individuals with the specified autoimmune disease compared to the incidence of cancer in the general population. A value greater than 1 indicates more incidence of cancer in the autoimmune group while a value less than 1 indicates less cancer in the autoimmune group. The number itself holds significant meaning, for example, a value of 2 suggests a twofold increased incidence while a value of 10 suggests a tenfold increased incidence.

Celiac disease
Celiac disease presents the strongest associations to gastrointestinal and lymphoproliferative cancers. In celiac disease, the autoimmune reaction is caused by the body’s loss of immune tolerance to ingested gluten, found primarily in wheat, barley, and rye. This explains the increased risk of gastrointestinal cancers, as the gastrointestinal tract includes the esophagus, stomach, small intestine, large intestine, rectum, and anus, all areas that the ingested gluten would traverse in digestion. The incidence of gastrointestinal cancer can be partially reduced or eliminated if a patient removes gluten from their diet. Additionally, celiac disease is correlated with lymphoproliferative cancers. Below are the specific cancers associated with celiac disease, as well as the standardized incidence ratios (SIR).


 * Any cancer – 1.3
 * Small intestine – 10, 25
 * Non-Hodgkin’s lymphoma – 6.3
 * Esophagus – 4.2
 * Stomach – 3
 * Liver – 2.7

Inflammatory bowel disease
Inflammatory bowel disease is associated with cancers of the gastrointestinal tract and some lymphoproliferative cancers. Inflammatory bowel disease (IBD) can be further categorized as Crohn's disease or ulcerative colitis. In both cases, individuals with IBD lose immune tolerance for normal bacteria present in the gut microbiome. In this case, the immune system attacks the bacteria and induces chronic inflammation, which has been linked to increased cancer risk. Below are the specific cancers associated with Crohn's disease and ulcerative colitis, as well as the standardized incidence ratios (SIR).

Crohn's disease

 * Any cancer – 1.54
 * Small intestine – 13.82, 11.05
 * Colorectal – 5.80
 * Anus – 3.1
 * Large intestine – 2.93, 2.76
 * Liver – 2.57
 * Non-Hodgkin’s lymphoma – 2.54

Ulcerative colitis

 * Any cancer – 1.46
 * Liver – 4.30
 * Small intestine – 2.42, 4.10
 * Large intestine – 3.60, 3.13
 * Rectum – 2.26

Multiple sclerosis
Multiple sclerosis is associated with decreased risk of cancer throughout the body but an increased risk of central nervous system cancer, primarily in the brain. Multiple sclerosis is a neurodegenerative disease in which T-cells – a specific type of immune cells – attack the important myelin sheath in brain neurons. This greatly reduces the nervous system function, creating inflammation and subsequent cancer of  the brain. The hyperactivity of the immune system is present throughout the body; however, it only causes chronic inflammation in the brain where the myelin sheath is present. Because of this, the immune system is able to react very sensitively in detecting and fighting off cancer throughout the body without inducing an autoimmune response. This is believed to explain the decreased incidence of systemic cancer throughout the body. Below are the specific cancers associated with multiple sclerosis as well as the hazard ratios (HR) that represent the likelihood of cancer development.


 * Any cancer – 0.91
 * Brain – 1.44
 * Gastrointestinal – 0.83
 * Prostate – 0.80
 * Lymphoma – 0.76
 * Lung – 0.69
 * Pancreatic – 0.67
 * Ovarian – 0.58

Rheumatoid arthritis
Rheumatoid arthritis presents mild, yet significant associations with focal cancers all throughout the body as well as lymphoproliferative cancers. In rheumatoid arthritis, cells that make up the body’s joints and cartilages become invasive and induce local inflammation. Additionally, the chronic inflammation and over-activation of the immune system creates an environment that favors further malignant transformation of other cells. This can explain the associations to cancer of the lungs and skin as well as the increased risk of other hematologic cancers none of which are directly affected by the inflammation of joints. Below are the specific cancers associated with rheumatoid arthritis as well as the standardized incidence ratios (SIR).


 * Any cancer – 1.12
 * Kidney – 2.12
 * Melanoma – 1.47
 * Lung – 1.36
 * Hematologic cancer – 1.07, 2.74
 * Non-Hodgkin’s lymphoma – 3.54
 * Hodgkin's lymphoma – 3.06

Systemic lupus erythematosus
Systemic lupus erythematosus is associated with focal cancers throughout the body and lymphoproliferative cancers. Systemic lupus erythematosus affects multiple organ systems and is characterized by a widespread loss of immune tolerance. The chronic inflammation throughout the entire body promotes the malignant transformation of other cells which contributes to the increased risk of systemic and lymphoproliferative cancers. Conversely, systemic lupus erythematosus is correlated with a decrease in some cancers. This is best explained by increased immunosurveillance in these areas, however, the mechanism for why these areas experience lower incidence is poorly understood. Below are the specific cancers associated with systemic lupus erythematosus as well as the standardized incidence ratios (SIR).


 * Any cancer – 1.14
 * Hematologic cancer – 4.96
 * Non-Hodgkin’s lymphoma – 2.74, 7.27
 * Diffuse large B-cell lymphoma – 3.26
 * Hodgkin's lymphoma – 3.02
 * Follicular lymphoma – 2.89
 * Leukemia – 2.13, 2.64
 * Kidney – 2.15, 3.99
 * Central nervous system – 3.30
 * Breast – 0.76
 * Prostate – 0.69
 * Melanoma – 0.67
 * Cervical – 0.55