Dermatomyositis is an autoimmune disease primarily affecting the muscles and skin. It can cause complications, including an increased risk of small cell lung cancer (SCLC) and other cancers.

Dermatomyositis can lead to muscle weakness and movement difficulties that gradually worsen. In contrast, SCLC is a highly aggressive type of lung cancer that grows quickly and can potentially spread to other body parts.

Interestingly, dermatomyositis and SCLC share a connection. Sometimes individuals with dermatomyositis may also develop SCLC, and vice versa. For some, dermatomyositis can be an early indicator of underlying SCLC. It’s important that anyone with dermatomyositis symptoms undergo a thorough medical assessment. A healthcare professional may also recommend ongoing monitoring.

This article explores the link between dermatomyositis and SCLC, the causes, and a person’s outlook.

A person with dermatomyositis and SCLC walking alongside their carer -1.Share on Pinterest
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Dermatomyositis (DM) is characterized by muscle inflammation (myositis) and a distinctive skin rash of purple or reddish patches on the face, neck, chest, shoulders, and back.

The condition can lead to muscle weakness, particularly in the hips, thighs, shoulders, and upper arms. Over time this leads to difficulty in the following activities:

  • climbing stairs
  • getting up from a seat
  • lifting objects

While the exact cause of DM is still unknown, experts believe it may involve an abnormal immune system response that mistakenly attacks healthy tissues in the body.

See pictures of DM lesions here.

There is a recognized association between DM and malignancies. Studies show that individuals with DM have a 6-fold higher risk of developing cancer than the general population, particularly in the 2 years following receiving a DM diagnosis.

Experts estimate that around 10–25% of people with DM also have some form of cancer, commonly lung cancer. DM co-occurs with lung cancer in around 1 in 10 cases.

How often do lung cancer patients develop DM?

Doctors typically associate DM with SCLC rather than non-small cell lung cancer (NSCLC), but that is not always the case.

In a retrospective 2023 research review involving 689 adults diagnosed with lung cancer, 97 people had SCLC, and 592 were diagnosed with NSCLC. Only one person in the entire study group had DM, and that individual had NSCLC. So even though there is a connection between the two diseases, the DM diagnosis is more predictive.

The exact reasons behind the association are not fully understood. More research is needed to establish a definitive relationship.

Experts remain unsure of the exact underlying mechanisms linking DM and SCLC, but it can include:

Paraneoplastic syndrome

One possible explanation for the link is the concept of paraneoplastic syndrome. Paraneoplastic syndromes are a group of disorders that occur due to an immune response to a tumor. In the case of DM and SCLC, the immune system’s response to the cancer cells in the lungs may trigger an abnormal immune reaction and lead to DM.

Some experts have found specific antibodies that attack healthy tissues may play a role. This includes an antibody that defends against TIF1-gamma called anti-TIF1-gamma antibodies. It targets markers primarily found in the muscles and skin. Around 84% of people with anti-TIF1-gamma antibodies have cancer-associate DM.

Usually, TIF1-gamma acts as a tumor suppressor and helps regulate cell growth. However, mutations in TIF1-gamma can lead to uncontrolled cell division.

Antibodies produced by the immune system directed against mutated TIF1-gamma proteins in cancer cells may mistakenly bind to normal TIF1-gamma receptors in healthy muscles and skin, triggering DM. This theory is called ‘molecular mimicry’ and can explain how SCLC triggers the autoimmune response of DM.

Genetic predisposition

Another theory focuses on shared genetic factors. Certain genetic predispositions may make individuals more susceptible to both DM and SCLC. This could help explain why some individuals with DM go on to develop SCLC, while others do not.

Furthermore, DM and SCLC may share risk factors such as smoking. Shared environmental factors and immune system dysregulation may contribute to the development of both conditions.

Yes, experts link DM with various cancers. These include:

  • ovarian
  • breast
  • prostate
  • kidney
  • blood cancers
  • gastrointestinal cancers

DM is a paraneoplastic response to cancer. It does not cause cancer.

DM treatment aims to manage inflammation and symptoms. While treating DM itself may not directly reduce the risk of developing SCLC, early detection and appropriate management of both conditions is beneficial.

For example, in a 2021 case study, doctors reported the individual experienced a significant improvement in DM symptoms after receiving chemotherapy and radiation treatment for SCLC. However, resolving DM symptoms does not mean the cancer is cured.

Therefore, it is crucial for healthcare professionals to carefully monitor DM cases to check for SCLC. Regular screenings and evaluation, using imaging and pulmonary function tests, may help detect SCLC earlier, potentially improving treatment options and a person’s outlook.

People with DM and cancer often have worse symptoms and a less optimistic outlook. When DM and cancer present together, they typically do not respond to corticosteroid treatment.

A 2019 study notes that people with DM may overlook the signs of lung cancer as they are nonspecific. As a result, doctors may diagnose the cancer at a more advanced stage when it is more challenging to treat.

Furthermore, a 2020 study conducted in China noted that the 5-year survival rate for those with DM is between 60% and 90%. But this drops to between 10% and 56% when the person also has cancer.

Dermatomyositis (DM) is a rare autoimmune condition primarily affecting the muscles and skin. DM can arise in individuals with a higher risk of developing cancer, including small cell lung cancer (SCLC).

The connection between the two diseases is not fully understood. However, research suggests a dysfunctional immune response to cancer cells is a likely contributor. There may also be shared risk factors such as smoking.

People with DM and SCLC typically have a less optimistic outlook, but working with their healthcare team to create a personalized treatment plan may help improve their outlook.