Myositis and cancer have been linked since 1916, but few in-depth clinical research studies have been published. The findings of those studies, however, show an increased incidence of cancer in patients with polymyositis and a significant increase for those with dermatomyositis.
Myositis does not cause cancer.
Cancer-Associated Myositis (CAM)
First, myositis does not cause cancer. However, researchers have found that a higher percentage of patients with myositis also develop cancer. Cancer-associated myositis (CAM) is malignancy that develops within a year or two of a diagnosis of myositis. In these patients, it is believed that the malignancy activates the immune system, which stimulates the development of the autoimmune disease.
Cancer-associated myositis occurs most frequently for those with dermatomyositis. Patients with polymyositis may develop cancer but generally about half as frequently as those with dermatomyositis. Those with necrotizing myopathy are still at higher risk than the general population, but this risk is much lower than with other forms of myositis. It is very rare for children and those with inclusion body myositis to develop cancer-associated myositis. After five years from the onset of myositis, rates of cancer for myositis patients are the same as for those of the general population
Cancer Risk and Risk Factors
The overall cancer rate varies between 9% and 32% for dermatomyositis (DM) patients, most often ovarian, lung, pancreatic, colorectal, and non-Hodgkin’s lymphoma. Most of these cancers occur after the onset of myositis symptoms, typically within the first 1 to 2 years, however colorectal and pancreatic cancer have been shown to occur later than 5 years.
The most common cancers seen in patients with DM include breast, colon, lung, ovarian, skin (melanoma), non-Hodgkin lymphoma (NHL), nasopharyngeal, and stomach.
The highest risk of developing cancer in patients with DM is within the first couple of years of myositis onset. Older patients and those with more severe findings on skin/muscle biopsy (cutaneous necrosis, capillary damage, and cutaneous leukocytoclastic vasculitis), prior history of cancer, and treatment resistance are at high risker of developing cancer within the DM population.
Approximately 15% of people with polymyositis (PM) are diagnosed with cancer, most often non-Hodgkin’s lymphoma, lung, and bladder. Some of these cancers (60-70%) are discovered after the onset of myositis. However, after one year post-diagnosis, the likelihood diminishes significantly, and by the 5th year post-diagnosis, the rate dropped to the cancer rate of the general population.
Risk factors for CAM include:
Previous history of cancer – If you have had cancer in the past, you are at higher risk for developing cancer with myositis.
Age at diagnosis – Those who are over 45 are at higher risk.
Family history of cancer – If your family has a history of cancer, you are at a higher risk of developing cancer.
Additional Cancer Risks
Not only do poly- and dermatomyositis come with a higher risk of cancer, but there are also other factors which increase the risk such as certain autoantibodies and medications used to treat myositis.
Myositis-specific and associated antibodies can provide insight into cancer risk. The presence of certain antibodies is linked with increased cancer risk, including those positive for TIF1-gamma (TIF1-γ) or NXP2. Testing positive for these, and others should alert your physician that you are at a higher risk of having cancer and to order the necessary cancer screenings.
Other autoantibodies which are currently known to be associated with increased cancer rates are P155/140 and Anti T1F1 (found in DM and JDM).
Patients positive for additional antibodies actually have a lower risk of developing malignancy (anti-SRP, antisynthetase, anti-Mi-2, anti-RNP, anti-Ku, and anti-PM-Scl).
Those with antisynthetase autoantibodies (most common is Anti-Jo-1 and others include Anti-PL-7, Anti-PL-12, Anti-EJ, Anti-OJ, Anti-KS, Anti-Ha, and Anti-Zo) are at a lower risk for developing cancer-associated myositis.
It is extremely rare for children and those with inclusion body myositis to develop cancer-associated myositis.
Immune Suppressing Medications (DMARDs)
In addition to the myositis associated myositis, there is a cancer connection with commonly used immunosuppressive medications such as Methotrexate, Imuran (Azathioprine), and CellCept (Mycophenolate), all of which show an increased incidence of non-Hodgkin’s lymphoma and lung cancers.
Methotrexate is also associated with melanoma, while non-melanoma skin cancers are seen more with Imuran and CellCept.Myositis Treatments
Suggested Cancer Screenings
In addition to the Myositis-Specific Antibodies (MSA) panel (which should be conducted as part of the myositis diagnosis and can show if cancer-related antibodies exist) regular Complete Blood Count (CBC), Comprehensive Metabolic Panel (CMP), and urinalysis (UA) should be conducted.
Patients should be up to date with all age and gender-appropriate screenings, such as mammography, pelvic exam, Pap test, and colonoscopy.
- Mammogram for all women over the age of 30
- Pelvic exam and Pap smear for all women
- Colonoscopy for patients over the age of 50
- Prostate-specific antigen (PSA) blood test for all men over the age of 50
- Basic chest x-ray
- Complete blood count (CBC) annually
- Skin cancer screening for all patients
- All age appropriate and doctor recommended cancer screenings
In addition to these the following cancer screening tests may be suggested:
In addition, patients who do not respond well to standard therapy, have severe skin ulcerations, and are losing weight should be followed closely for signs of malignancy.
After five years, cancer screenings usually follow the usual age- and gender-appropriate recommendations for the general population. Even if the cancer has been treated, it can recur, so screening should continue.
If myositis symptoms return after a period of remission, it is possible that the cancer has returned and cancer screenings should be done again.
NOTE: The statistics included are from research done in early 2016 and, depending on when you are reading this, may no longer be accurate. Be sure you also contact your physician should you have questions, concerns, or before deciding on a treatment due to risks shown here. This is for informational purposes only.
Usually, the first goal in treating cancer-associated myositis is to treat the cancer itself. For some, this is the answer and the myositis may also go into remission. Remember, there is no cure for myositis, but remission is possible for many.
For others, the myositis will continue to be a challenging autoimmune disease, and like other forms of myositis, must be treated with the standard therapies including immunosuppression drugs. Treating both the cancer and myositis simultaneously can be complicated as cancer treatments often involve suppressing the immune system, at times using the same medications used to treat myositis.
Standard treatments for myositis should continue as usual. Those who stop treatment prematurely often experience significant worsening of their myositis symptoms that may be difficult to treat.
More reading about Cancer and Myositis
“Simply Put” is a service of Myositis Support and Understanding, to provide overviews of Myositis-related medical and scientific information in understandable language.
MSU volunteers, who have no medical background, read and analyze often-complicated medical information and present it in more simplified terms so that readers have a starting point for further investigation and consultation with healthcare providers. The information provided is not meant to be medical advice of any type.