Dermatomyositis is an inflammatory disease that mainly affects the muscles and skin. While there’s no cure for dermatomyositis, the condition can be managed through measures like medications and physical therapy.

Having dermatomyositis is associated with various complications and risks. One of these is an increased likelihood of developing cancers, including small cell lung cancer (SCLC).

In this article, we take a closer look at dermatomyositis, its association with SCLC, and more.

Dermatomyositis (DM) is a type of condition called an inflammatory myopathy, which is marked by muscle inflammation and weakness. It’s believed to be an autoimmune disease, which is when the immune system attacks healthy tissues.

What causes DM is unknown, but is thought to be a combination of genetic and environmental factors. What we do know is that DM is very rare. It’s estimated to occur in only 9.63 out of 1 million people.

Symptoms of dermatomyositis

One of the main symptoms of DM is muscle weakness. This tends to get worse over time and most often affects muscles close to your core, such as those of the neck, shoulders and upper arms, and hips.

As it worsens, muscle weakness can begin to impact certain movements, such as walking, climbing stairs, or lifting your arms over your head. When muscles in the neck are affected, it can lead to trouble talking or swallowing.

In addition to muscle symptoms, people with DM also have a variety of skin symptoms, including:

Other potential symptoms of DM include:

People with DM are estimated to have a 6-fold higher risk of developing cancer compared with the general population. In fact, it’s estimated that 10% to 25% of DM cases are associated with cancer.

Cancer is often diagnosed at the same time as DM or shortly after. The risk is highest in the first year after a DM diagnosis and continues to be so for up to 5 years. However, even after this, people with DM still have a high cancer risk compared with the general population.

Lung cancer is often linked with DM. A small older study found that the most common type of lung cancer associated with DM was SCLC.

SCLC is one of two main types of lung cancer, making up about 10% to 15% of all lung cancers. It often grows and spreads faster than non-small cell lung cancer (NSCLC), the other main type of lung cancer.

What’s the link between dermatomyositis and small cell lung cancer?

The exact cause-and-effect link between DM and cancer, including SCLC, isn’t fully understood.

Some experts believe that DM is a type of paraneoplastic syndrome. Paraneoplastic syndromes often happen when there’s a dysfunctional immune response to a tumor. They can also occur when a tumor produces a hormone or other peptide. Here’s an example of how that might happen with DM:

  1. DM is associated with the presence of various antibodies that attack healthy tissue. One of these is an antibody against TIF1-gamma. This antibody targets markers that are mainly present in the muscles and skin.
  2. Normally, the TIF1-gamma protein in your body is a tumor suppressor, meaning it’s involved in inhibiting cell growth. However, when it becomes mutated it can mean that cells are free to grow and divide out of control.
  3. It’s possible that antibodies to mutated TIF1-gamma proteins in cancer cells could cross-react with normal TIF1-gamma proteins in the muscles and skin, leading to DM. This could explain why DM and cancer often happen so closely together.
  4. Anti-TIF1-gamma antibodies are associated with the development of cancer in DM. In fact, up to 84% of people with anti-TIF1-gamma antibodies have DM that’s associated with cancer.

In addition to SCLC, DM is linked to several other types of cancer. These include:

Some factors may increase the risk of cancer for people with DM. These include:

  • being 45 years and older at DM diagnosis
  • being assigned male at birth
  • experiencing severe DM symptoms
  • having trouble swallowing as a DM symptom
  • having anti-TIF1-gamma antibodies
  • having DM that’s resistant to standard treatments

DM itself is often treated with corticosteroids. These are drugs that reduce the level of inflammation in the body.

If necessary, other immunosuppressants like methotrexate and azathioprine may also be used for DM. These types of immunosuppressants broadly dampen the immune response.

In situations where DM and SCLC occur together, DM may be treated briefly first. Then cancer treatment for SCLC is started, which typically includes one or a combination of surgery, chemotherapy, or radiation therapy.

A 2022 case study also found that chemotherapy with the immunotherapy drug atezolizumab (Tecentriq) may be beneficial for DM-associated SCLC with anti-TIF1-gamma antibodies. After treatment, symptoms improved and tumor size decreased.

The outlook for DM and cancer is generally poor. A 2019 study notes that lung cancer signs in people with DM may be nonspecific and overlooked. Due to this, cancer may be diagnosed at more advanced stages when it has spread and is more difficult to treat.

A 2020 study notes that previous research has found that the 5-year survival rate of people with DM is between 60% and 90%. When DM is associated with cancer, this falls to between 10% and 56%.

Because DM and cancer can be closely linked, treating the cancer can reduce DM symptoms in some situations. For example, a 2021 case study reports resolution of DM symptoms after chemotherapy and radiation treatment for SCLC.

However, even if DM symptoms resolve, it doesn’t mean that the cancer will go away as well. SCLC is often more aggressive than other types of lung cancer. According to the American Cancer Society (ACS), the 5-year survival rates are:

  • 29% for SCLC that remains localized to the lung
  • 18% for SCLC that’s spread to nearby tissues or lymph nodes
  • 3% for SCLC that’s spread to more distant tissues (metastasized)
  • 7% overall

Besides the type of cancer and health conditions like DM, other factors are important for outlook as well, such as the cancer’s stage, grade, and your age. Your care team can provide you with a better estimate of your individual outlook.

Dermatomyositis (DM) is a condition that happens when your immune system mistakenly attacks your muscles and skin. It’s also associated with an increased risk of cancer, including lung cancers like SCLC.

The exact connection between DM and cancers like SCLC is unknown. However, it’s possible that a dysfunctional immune response to cancerous changes contributes to the link between the two conditions.

Overall, the outlook for SCLC and DM is poor. However, it’s important to talk with your healthcare team regarding individual treatment recommendations and outlook.