While myositis doesn’t cause cancer, researchers have found that a higher than normal 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 patients with dermatomyositis. (It has been estimated that as much as 20-30% of DM patients will develop cancer.) Those with polymyositis develop cancer about half as frequently as those with dermatomyositis. Patients 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.
Risk factors for cancer-associated myositis include the following:
Older age of onset of myositis – Patients older than 45 are at higher risk.
A previous history of cancer – If you have had cancer in the past, you are at higher risk for developing cancer with myositis.
A family history of cancer – If someone in your family has had cancer, you are at a higher risk of developing cancer, which includes cancer associated with myositis.
The presence of certain autoantibodies – Those who have TIF1-gamma (TIF1-γ) or NXP2 autoantibodies in their blood are at higher risk than other myositis patients to develop cancer-associated myositis.
Patients who have rapid onset of disease and poor response to treatment are at higher risk.
The good news is, those with antisynthetase autoantibodies (the most common is Anti-Jo-1; others include Anti-PL-7, Anti-PL-12, Anti-EJ, Anti-OJ, Anti-KS, Anti-Ha, and Anti-Zo) are at lower risk for developing cancer associated with myositis.
Cancers associated with myositis
Patients with dermatomyositis are at greater risk for the following cancers:
- Non-Hodgkin lymphoma
Patients with polymyositis are at greater risk for the following cancers:
- Non-Hodgkin lymphoma
Cancer screening recommendations
Early detection is the key to treating cancer effectively. It is recommended that all newly diagnosed myositis patients, especially those who are at increased risk for cancer, should be followed closely for cancer for at least five years. This includes the following basic screening procedures based on age and gender:
- 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
For patients at higher risk, especially those with at-risk autoantibodies, the following additional screening procedures are recommended:
- CT scan of chest, pelvis, and abdomen
- PET scan for those with anit-TIF1-γ and over the age of 50
- Pelvic ultrasound for women
In addition, patients who are not responding well to standard therapy, have severe skin ulcerations, and are losing weight should be followed more closely for signs of malignancy.
After five years, screening procedures should follow the usual age- and gender-appropriate recommendations for all people. 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 as well. Cancer screenings should be done again at this time.
With CAM, cancer and myositis are often diagnosed around the same time. It is thought that, in this case, cancer is providing some stimulus for the inflammatory disease. The cancer, therefore, needs to be treated or removed in order for the myositis to improve.
While the myositis may improve when the cancer is treated, however, it does not necessarily go into remission. The myositis is still present as an autoimmune disease and must still be treated with immunosuppressants. In this way, treatment of both the cancer and myositis go hand-in-hand.
Standard treatments for myositis should continue as usual; they should not be decreased or stopped early because the cancer has been treated. Patients with CAM who discontinue myositis treatment prematurely often experience significant worsening of myositis symptoms that may be difficult to treat.
Treating myositis while also treating cancer can be tricky. Cancer treatment often involves immune suppression, sometimes using the same drugs used to treat myositis. Cyclophosphamide (Cytoxan), for example, is a chemotherapy agent that is sometimes used to treat refractory lung disease in myositis patients. If this drug is being used to treat cancer, it and other drugs like it should not also be used to treat myositis.
During cancer treatment, the best medications for treating myositis are those that do not increase the effects of chemotherapy drugs. These include corticosteroids (for example, prednisone) and immunoglobulin (for example, IVIg or SCIg).
Additional information about cancer-associated myositis can be found in the Myositis Library section of this website.
Myositis and malignancy – video presentation by TMA medical advisor Dr. Rohit Aggarwal at the 2017 TMA Annual Conference