What is lung cancer and how does it kill?

By a first-year Medical Student at Cambridge

Introduction:


Lung cancer is the most common cause of cancer death in the UK, accounting for 20.9% of all deaths from cancer in 2013. As a result, lung cancer has a large impact on national mortality; in 2013 the disease accounted for 6% of all deaths in the UK.

The table below, from the Office for National Statistics, shows the leading causes of death in the UK in 2012 and lung cancer is ranked the second leading cause of death in men and the sixth leading cause of death in women; accounting for a total of 30,273 deaths in one year. Figure 1: Leading causes of death in England and Wales, 2012


This essay aims to establish clear reasons as to why lung cancer is such a common cause of death in the UK. In order to do this, I will examine the various risk factors associated with the different forms of lung cancer and determine their relative prevalences in the UK, look at the healthcare system currently in place to discover any inadequacies that may be to blame for such a high mortality rate of lung cancer and, finally, look at current treatments for the disease and analyse their effectiveness. Whilst doing all these things, I will comment on what more could be done to reduce the number of deaths from this seemingly deadly disease.


First of all, however, we must understand what exactly lung cancer is and how it causes death. This first section looks at the different types of lung cancer, how lung tumours may form and how they eventually kill.


What is Lung Cancer and how does it kill? A good definition of cancer is “a group of diseases characterised by unregulated cell growth and the invasion and spread of cells from the site of origin to other sites in the body.”[1] In lung cancer, the unregulated cell growth takes place in tissues of the lung and the growth can spread to other sites in the body.

Cancer that begins in the lungs is called primary lung cancer and cancer that begins in another part of the body and then spreads to the lungs is called secondary lung cancer.

There are two main types of primary lung cancer: non-small cell lung cancer and small-cell lung cancer [2].

Small cell lung cancer (SCLC) is so named because of the size of the cancer cells when looked at under a microscope. This type of lung cancer often starts in the bronchi and then spreads throughout the body very quickly; meaning the cancer is often at an advanced stage when diagnosed, resulting in a poor prognosis for the patient.[3]

Non-small cell lung cancer (NSCLC) consists of three main types: squamous cell carcinoma, adenocarcinoma and large cell carcinoma. Each subtype is different in its rate of growth/spread and type of cell it usually begins with but they are grouped together under NSCLC because the approach to treatment and their prognoses are often very similar.[4]

Having briefly looked at the typing of lung cancer, let us now look at how lung cancer actually kills.

A recent study examining 100 people with lung cancer found that the following were some of the immediate and contributing causes of death in patients with lung cancer: [5]

1.1. Tumour Burden

- The physical presence of a tumour, often causing impairment of organ function, was identified as the cause of death in 30% of people with lung cancer. This statistic was further broken down to 4 people dying from “tumour burden” in the lungs (causing respiratory failure) and the other 26 due to “tumour burden” from metastases.

1.2. Infections

- Infections were responsible for death in 20% of the patients. For 12 of these patients, the infection was pneumonia and for 8 the infection was sepsis. These infections can come about when part of the lung collapses due to a tumour blocking that part. [6]


1.3. Complications of metastatic disease

- When cancer metastasises to other organs, the normal functioning of that organ is compromised. For example, if cancer spreads to the liver, the ability of the liver to remove toxins from the body may be affected. Thus, the build-up of toxins may cause death. In the study, complications of metastatic disease accounted for 18% of all deaths with 9 patients dying from cardiac metastases, 3 from liver metastases and 3 from brain metastases.

1.4. Pulmonary Haemorrhage

- Pulmonary haemorrhage (bleeding into the lungs) was responsible for 12% of deaths. Such bleeding can occur when a tumour grows to a point where it impinges on a blood vessel in the lungs; causing the vessel to burst.

1.5. Pulmonary Embolism - This is where a thrombus (usually from the leg) breaks off, travels to the lungs and lodges in a pulmonary artery. This causes a build-up of pressure within the pulmonary artery. If the artery is completely blocked, the pressure within the vessel would become so great so that the pressure in the right ventricle could never exceed it; meaning that no blood would be pumped to the lungs. In effect, the heart stops beating and the patient dies. [7] In the study, 10% of lung cancer deaths were caused by pulmonary emboli. This percentage may be so high because cancer patients are more susceptible to having blood clots due to them having a higher number of platelets and clotting factors in their blood [8]. In addition, cancer patients may be quite inactive; allowing clots to develop.

Obviously, this one study examining a sample of only 100 patients cannot be representative of all lung cancer deaths and other causes of death in patients with lung cancer may include various iatrogenic complications, such as side effects of chemotherapy/radiotherapy or complications in surgery (eg – bleeding of patient).

So, we can see that lung cancer can kill in many ways and this is, perhaps, one of the reasons why it is such a common cause of death; any one of the above conditions is sufficient to cause the death of a patient.

Now, we must now turn to look at the risk factors associated with lung cancer and examine their respective prevalences in the UK to determine whether a prevalence of risk factors is a reason for lung cancer being such a common cause of death. Check out part 2 of this series for more information.

Further Reading:

[1] Pecorino, L. (2012). Introduction. In: Molecular Biology of Cancer. Oxford: Oxford University Press. p2. [2] (2013). Lung Cancer. Available: http://www.nhs.uk/conditions/Cancer-of-the-lung/Pages/Introduction.aspx. Last accessed 10th August 2014. [3] (2013). Lung Cancer (Non-Small Cell). Available: http://www.cancer.org/cancer/lungcancer-non- smallcell/detailedguide/non-small-cell-lung-cancer-what-is-non-small-cell-lung-cancer. Last accessed 17th August 2014. [4] ibid [5] Nichols L, Saunders R, Knollmann FD. (2012). Causes of death of patients with lung cancer. Archives of Pathology and Laboratory Medicine. 136 (12), 1552-7. [6] (2014). How can cancer kill you?. Available: http://www.cancerresearchuk.org/cancer-help/about- cancer/cancer-questions/how-can-cancer-kill-you. Last accessed 19th August 2014.

[7] ibid [8] (2014). Cancer and the risk of blood clots. Available: http://www.cancerresearchuk.org/cancer-help/about- cancer/cancer-questions/cancer-and-the-risk-of-blood-clots. Last accessed 19th August 2014.