Pneumonia and lung cancer both occur in the lungs and share several overlapping symptoms. Lung cancer can also increase the risk of pneumonia by weakening the immune system.

Pneumonia is a lung infection that leads to breathing difficulties and fluid in the lungs. Various viruses, bacteria, and fungi can cause pneumonia.

Lung cancer develops due to the overgrowth of cells in the lung that can form tumors. According to the American Cancer Society (ACS), lung cancer is the second most common form of cancer in the United States, as well as the leading cause of cancer death.

In this article, we look at the link between lung cancer and pneumonia and their effects on the body.

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Lung cancer often does not cause symptoms until its later stages. However, pneumonia can develop as a complication of lung cancer.

Individuals who have a weakened immune system are vulnerable, particularly, to developing pneumonia. For this reason, 50–70% of people with lung cancer develop serious lung infections, such as pneumonia, during their illness.

Additionally, the intensive therapies that doctors use to treat lung cancer often severely reduce immune function. This means that people may be less able to prevent infectious agents from entering their body. They may also have more difficulties in fighting infection and may not respond well to medications

For these people, infections are a serious health risk. Infection is currently the second most common cause of death outside of the tumors among people with lung cancer.

A weaker immune system also accounts for pneumonia’s significant impact on very young people and older adults.

More information about lung cancer is available here.

Lung cancer does not always cause symptoms. However, when it does, they usually occur when the cancer has reached an advanced stage.

Some lung cancer and pneumonia symptoms overlap. Typically, the symptoms of pneumonia are more immediately severe. Lung cancer generally develops more slowly and does not cause symptoms until it reaches an advanced stage.

Overlapping symptoms include:

  • Coughing: This tends to be more persistent in people with lung cancer. It will usually last for several weeks and get progressively worse.
  • Phlegm: This is generally dark red, brown, yellow, or green.
  • Shortness of breath: This is more persistent in people with lung cancer than those with pneumonia. However, people with pneumonia experience more acute breathlessness that may progress more quickly without treatment.
  • Stabbing chest pains: These get worse during a breath or a cough.
  • Tiredness: People with lung cancer commonly feel more fatigue than those with pneumonia.
  • Loss of appetite: People with lung cancer tend to experience loss of appetite, which may result in weight loss.
  • Wheezing: This is rare in both lung cancer and pneumonia.

Other symptoms include:

  • fever
  • rapid heartbeat
  • hot and cold flushes
  • headaches
  • nausea or vomiting
  • joint or muscle aches
  • confusion
  • coughing up blood
  • higher
  • persistent chest infections

A doctor will generally not use specific symptoms to distinguish between lung cancer and pneumonia. They will focus more closely on how rapidly symptoms develop and the timing of their onset.

Lung cancer symptoms

Common symptoms that occur only in people with lung cancer include:

Less common symptoms include:

  • swelling in the face or neck
  • long lasting shoulder or neck pain
  • difficulty swallowing
  • hoarseness
  • changes in the shape of the fingertips

Find out more about lung cancer here.

Any individual can develop both pneumonia and lung cancer. However, some factors make it more likely to develop these health problems.

Lung cancer itself is a risk factor for pneumonia. Receiving chemotherapy treatment for lung cancer might also increase a person’s pneumonia risk by reducing immune activity.

Smoking tobacco is a significant risk factor for developing lung cancer, especially over an extended period. It also contributes to pneumonia risk.

Other risk factors for lung cancer include:

  • exposure to carcinogenic chemicals, such as radon, asbestos, and uranium
  • a family history of lung cancer
  • previous radiation therapy to the chest
  • air pollution, which some researchers suggest is responsible for 5% of global lung cancer deaths

The following factors can increase the risk of pneumonia:

  • chronic lung diseases, such as chronic obstructive pulmonary disease (COPD) or cystic fibrosis (CF)
  • chronic illnesses in other parts of the body, such as diabetes and heart disease
  • a repressed immune system, which may occur due to chemotherapy treatment for cancer, HIV, organ transplants, or using steroid medications over a long period
  • recent respiratory infection with a virus, such as flu
  • staying in a hospital, especially when using a ventilator
  • drug and alcohol abuse, which can increase the risk of a specific type known as aspiration pneumonia

Want to quit smoking? Learn more here.

When diagnosing pneumonia, a doctor may carry out a physical examination to check for swollen glands, abnormal breathing, or a high temperature.

A doctor will often confirm the diagnosis using an X-ray to show fluid build-up in the lungs.

Treatment will vary according to the type of pneumonia a person has and their overall health. Some people can treat pneumonia at home with plenty of fluids, rest, and medication.

People with more severe pneumonia may need to stay in the hospital to receive intravenous (IV) fluids and antibiotics. They may also require oxygen therapy or breathing assistance.

It is more difficult for a doctor to diagnose lung cancer. A chest X-ray can provide some information, but a biopsy is often necessary to confirm the diagnosis.

If a doctor confirms a diagnosis of lung cancer, they will request further tests, including a PET scan. This can help them assess how far the cancer has spread.

They will also order a biopsy. A specialist takes a small tissue sample and sends it for examination under a microscope.

Typically, a doctor inserts a small tube into the lungs through the nose or mouth to collect this sample. They will typically use a CT scan to guide the biopsy.

The results of these tests will determine the type of lung cancer, the location of the primary tumor, and the stage of the disease.

The doctor will use this information as well as the overall health of the individual to determine the most effective treatment approach.

Treatments will aim to cure, control, or ease symptoms. The options available can range from basic surgical procedures to chemotherapy or radiotherapy, depending on the severity of the lung cancer.

Here, learn about the different types of lung cancer biopsy.

The majority of pneumonia cases are not severe, although the illness is serious.

The duration of symptoms depends on the person’s overall health and the type of pneumonia they have.

Pneumonia can take several weeks to resolve. Without treatment, vital organs, such as the heart and brain, may not receive enough oxygen. This can lead to confusion, coma, heart failure, or even death.

The outlook for lung cancer tends to be worse than pneumonia regardless of treatment. However, if pneumonia is left untreated, it can result in death.

Identifying lung cancer at an early stage increases the chance of surgically removing the tumors before they spread. This gives a person a good chance of recovery.

However, according to the American Lung Association, only 16% of people with lung cancer receive a diagnosis before it spreads.

If the cancer spreads, or metastasizes, to distant organs in the body, the likelihood of surviving for 5 years is less than 5%. Over half of all people with this type of cancer do not survive for longer than one year, according to the American Lung Association.

Read about the different stages of lung cancer here.