Pneumonia and lung cancer both occur in the lungs and share a number of overlapping symptoms.

Pneumonia is a lung infection commonly caused by bacteria, a virus, or a fungus. Lung cancer is a harmful tumor often caused by smoking tobacco.

This article will discuss how lung cancer and pneumonia affect the body, how each condition is diagnosed, treated, and their relative outlooks.

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A weakened immune system may make pneumonia deadly for very young and older people.

What is pneumonia?

The nose and airways are very effective at preventing airborne germs from entering the lungs. Germs that cause pneumonia can sometimes slip through this defence, or spread from another part of the body to infect the lungs.

The germs that cause pneumonia can be derived from a range of bacteria, viruses, fungi, or certain chemicals. The severity of an infection varies depending on its cause.

The most common types of pneumonia are bacterial pneumonia and viral pneumonia, both of which can occur at the same time.

When the infection spreads to the bottom of the lungs, the tiny air sacs that allow oxygen to be passed into the bloodstream fill up with liquid. The air sacs are then unable to work properly. Less oxygen is then transferred out of the lungs and more waste carbon dioxide remains in circulation.

What is lung cancer?

Cancer is produced by a mutation in cell DNA that causes cells to function abnormally and multiply uncontrollably. These cancerous cells can grow to form tumors that disrupt normal body functioning.

Lung cancer is the second most common form of cancer in the United States behind breast cancer. It occurs when cancerous cells arise in one or both lungs.

It is possible for cells to become cancerous as a result of normal aging but lung cancer is most often caused by environmental factors.

Between 80-90 percent of lung cancer cases are caused by smoking tobacco. The disease can also be triggered by exposure to other chemicals including radon or asbestos.

Who is most at risk?

Both pneumonia and lung cancer can occur in anyone, but some individuals are more prone than others to develop one of these conditions.

Smoking tobacco is a major risk factor for developing lung cancer. Longer periods of smoking significantly increase the risk.

Individuals who have a weakened immune system are vulnerable, particularly, to developing pneumonia. This is why the very young and older people are more likely to develop pneumonia than other age groups.

It is also why an estimated 50-70 percent of people with lung cancer develop serious lung infections, such as pneumonia, during the course of their illness.

Additionally, the aggressive therapies that are used to treat lung cancer often leave people with severely weakened immune systems. This means they are:

  • less able to prevent germs from entering their bodies
  • not as well equipped to fight off infection or respond to medications

In these cases, infections are a serious health risk. Pneumonia is currently the second biggest killer of lung cancer patients after the cancerous tumors themselves.

A weakened immune system is also the reason why pneumonia is especially severe and sometimes deadly in very young and older people.

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Coughing and shortness of breath are symptoms that may be common to both lung cancer and pneumonia.

Telling pneumonia and lung cancer apart can be difficult at times as there is an overlap of some of the symptoms. Typically, the symptoms of lung cancer are the more severe.

Overlapping symptoms of pneumonia and lung cancer include:

  • Coughing: In lung cancer, this tends to be more persistent, lasting several weeks and progressively worsening.
  • Phlegm: This is usually dark red, brown, yellow, or green.
  • Shortness of breath: This is more persistent in lung cancer than with pneumonia.
  • Stabbing chest pains: These get worse when breathing or coughing.
  • Tiredness: More common in lung cancer than in pneumonia.
  • Loss of appetite: In lung cancer, this is often coupled with weight loss.
  • Wheezing: Less common in both conditions.

Additional common symptoms only linked with pneumonia include:

  • fever
  • rapid heartbeat
  • hot and cold flushes

Less common symptoms only linked with pneumonia include:

  • headaches
  • nausea or vomiting
  • joint or muscle aches
  • confusion

Additional common symptoms only associated with lung cancer include:

  • coughing up blood
  • persistent chest infections

Less common symptoms only associated with lung cancer include:

  • swelling in the face or neck
  • lasting shoulder or neck pain
  • difficulty swallowing
  • a hoarse voice
  • high temperature
  • change in the shape of finger tips

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An X-ray may be used to diagnose pneumonia and lung cancer.

Diagnosis of pneumonia may involve a physical examination to check for swollen glands, abnormal breathing, or a high temperature. A diagnosis will often be confirmed using a blood test or an X-ray to show any fluid buildup in the lungs.

Treating pneumonia will vary according to the type of pneumonia and the person's general health. In most cases, pneumonia can be treated at home with plenty of fluids, rest, and medication.

In more severe cases, hospital treatment may be required so fluids and antibiotics can be given intravenously. Oxygen therapy or breathing assistance may also be required.

Diagnosing lung cancer can be more difficult. A chest X-ray can provide a quick and simple check, but a computerised tomography (CT) scan is necessary to confirm the diagnosis.

If lung cancer is confirmed, further tests may be carried out including a positron emission tomography-CT (PET-CT) scan to locate all the cancerous cells.

A biopsy will also be conducted, whereby a small tissue sample is taken from the lungs and examined under a microscope.

Commonly, the tissue is taken by way of a small tube that reaches the lungs through the nose or mouth. This procedure is known as a bronchoscopy.

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

This information will be used to work out the most effective treatment approach after consideration of the general health of the person.

Treatments will aim to cure, control, or ease symptoms. The options available can range from basic surgical procedures to chemotherapy or radiotherapy depending on how severe the person's condition is.

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

The length of time symptoms may last depends on the individual's health and the type of pneumonia it is.

Bacterial pneumonia symptoms will typically go away after 1-3 weeks. Mycoplasma pneumonia can take 4-6 weeks, and viral pneumonia can last even longer.

If pneumonia is left untreated, vital organs like the heart and brain may not receive enough oxygen. The consequence of this can be confusion, coma, heart failure or even death.

The outlook for lung cancer tends to be the more severe regardless of treatment.

If the cancer is diagnosed at an early stage there is a chance it can be surgically removed while it is small and has not spread. This gives a good chance of recovery.

However, many patients with lung cancer are diagnosed after the cancer has already spread. In these cases, removing it is unlikely. Treatments will instead focus on limiting it progression and alleviating the symptoms.