Cancer is a disease that arises because of the uncontrollable growth of body cells due to gene damage. This is most commonly due to errors in the cell cycle and mitosis. The groups of cells generated from this unrestrained proliferation are called tumours, and they can be either benign or malignant. Oncology is the study of cancer.
Development of cancerous cells
Cancer develops during the cell cycle's interphase (preparation for mitosis). The DNA is copied and replicated during the synthesis stage (S phase). When the chromosomes are replicated, harmful errors can occur, altering the sequence of nucleotides. These errors are known as mutations. Most mutated cells die; however, those that survive will be capable of dividing to make clones. Another possibility is that cells enter mitosis uncontrollably due to epigenetic changes in the DNA.
To know more about how epigenetic changes can cause diseases, refer to our article, "Epigenetics and Disease".
Interphase includes the G1, S (synthesis) and G2 phases. This is where the cell grows and prepares for mitosis.
There are two main types of genes that, when mutated, can lead to cancer:
Tumour suppressor genes regulate cell division, repair mutated or damaged DNA, and initiate apoptosis (programmed cell death) if the damaged DNA is unrepairable. Cell division can no longer be tightly controlled when mutations occur in these genes as the genes are silenced or work poorly. In other words, when mutations occur in the DNA, they cannot be repaired or removed. As a result, these cells enter mitosis uncontrollably.
Silenced genes are inactivated genes. This means the gene product is no longer synthesised.
Oncogenes, however, are overactive genes that stimulate entry into mitosis—for example, some oncogenes code for growth factors. As the oncogene is overactive, the growth factor is synthesised in excess, which triggers the continual entry into mitosis. In the previous stage for these genes, when they are working correctly and inducing mitosis at a healthy rate, they are called proto-oncogenes.
Figure 1. Gene regulation of the cell cycle. Source: Finty Royle - StudySmarter Originals.
Benign and malignant tumours
There are two types of tumours: benign (non-cancerous) and malignant (cancerous). We will explore the differences of each tumour type in this section.
An agent that causes cancer is a carcinogen. Examples of carcinogens include asbestos, ultraviolet (UV) radiation, cigarette smoke, etc.
Benign tumours
Benign tumours are a mass of localised cells in one area that will not invade nearby tissues. These are called primary tumours. For this reason, they are not normally seen as life-threatening. However, they can become a problem if they press on blood vessels or nerves. In this case, the tumour is removed surgically or treated with medication or radiation.
So, how do patients develop a benign tumour in the first place? There can be different causes; some of the main reasons include:
- Diet
- Genetics
- Exposure to radiation
- Inflammation or infection
Examples of benign tumours
- Fibromas - these originate from fibrous or connective tissues.
- Adenomas - these originate from the glandular (epithelial) tissue: epithelial tissue lines the skin, glands and other parts of the body.
- Lipomas - these originate in fat cells between the skin and the muscle tissue.
- Myomas - these originate in muscle tissue, for example, in or around the uterus and the stomach. Myomas are also referred to as fibroids.
Malignant tumours
Malignant tumours are composed of cells that can break off and spread to distant sites (metastasis). They will spread through the body via the lymphatic system or the bloodstream. When the tumour moves through the lymphatic system, it can either empty into the bloodstream or end up in the lymph nodes. But most often, tumours will move through the bloodstream and establish secondary tumours at new sites.
Features of the lymph node:
- Lymph fluid flows into the node through the narrow vessels and flows out of the node through wider vessels.
- Valves are present to stop prevent flow in the wrong direction.
- B and T white blood cells are densely packed in the lymph nodes.
How can cancer be detected?
Cancer can be diagnosed in several ways. Cancer screenings for particular cancers, such as prostate cancer, can help diagnose them early. However, for other cancers, only at-risk groups will receive diagnostic screenings.
Detecting cancer early is important for increased treatment success rates.
Examples of exams to detect cancer
- Laboratory tests - body fluids (blood and urine) and tissue samples can be tested to detect tumour markers (proteins produced by the cancerous cells).
- Imaging tests - computerised tomography (CT) scans (a series of X-ray images) and magnetic resonance imaging (MRI).
- Biopsy - a cancerous tissue sample is removed and examined under a microscope.
- Endoscopy - a lighted tube is inserted to examine the inside of the body.
- Physical tests - the body is examined for indicators such as skin colour changes (skin cancer) or abnormal lumps (breast cancer).
In 1951, cancerous cells were taken from the cervix of Henrietta Lacks (hence HeLa). The cell line originating from Henrietta was made immortal and lives to this day. Usually, cancerous cells will only survive a couple of days, unlike the ones from Henrietta. The HeLa cell line is widely used in research for cancer treatments, gene mapping and others.
Examples of cancer
There are many types of cancers, and some of the most common types will be covered in this section.
Skin cancer
Skin cancer is the most common type of cancer. Skin cancer is most often caused by UV light which can damage the DNA in skin cells. Any changes or growths in the skin can be signs of skin cancer. This includes red or discoloured patches, changes of moles and open sores. Melanoma is a type of skin cancer that starts in the melanocytes, and it is the most dangerous form.
Melanocytes are skin cells that synthesise the pigment melanin.
Bowel cancer
Bowel cancer begins in the large bowels. Patients manifest symptoms such as abdominal pain and blood in faeces. Factors increasing the risk of getting bowel cancer include age, diet and alcohol consumption.
Ovarian cancer
Ovarian cancer originates in female ovaries. Some of the risk factors include genetics, hormone replacement therapy and endometriosis. The symptoms can sometimes resemble those in people suffering from irritable bowel syndrome (IBS), including bloating, pelvic pain and urinating very frequently.
Endometriosis occurs when tissue resembling the womb lining begins to grow abnormally in the ovaries and fallopian tubes.
Pancreatic cancer
Pancreatic cancer develops in the pancreas. Symptoms include jaundice, tiredness, temperature and effects on digestion, such as constipation. The risk factors include genetics and excessive alcohol consumption.
Jaundice is a condition in which the skin and whites of the eyes turn yellow.
Prostate cancer
Prostate cancer is the cancer of the prostate. Symptoms include pain during urinating, feeling that the bladder is not empty after urinating, blood in urine or semen and erectile dysfunction.
Prostate cancer develops slowly, and patients may not display symptoms for years. The causes of prostate cancer are not well-known, but obesity and genetics seem to play the biggest role.
Cancer treatment
Cancer treatments will differ depending on the type of cancer and its progression in the body. Genes, proteins, and other relevant substances will be tested for biomarkers to understand the person’s condition better.
Some patients may even enrol in clinical trials, where they will receive new treatments that are considered effective.
Examples of cancer treatments include:
- Chemotherapy - drugs can stop or slow the growth of cancerous cells. During chemotherapy, healthy cells will be killed, and their growth will slow. This causes multiple side effects such as extreme fatigue, vomiting and hair loss.
- Radiotherapy - radiation (internal or external) is delivered and aimed at cancerous cells to destroy them.
- Stem cell (bone marrow) transplant - replacement of diseased bone marrow.
- Surgery - tumours can be surgically removed.
- Immunotherapy - the use of the immune system to recognise the proteins on the surface of cancer cells. This includes adoptive T cell therapy (the transfer of T cells into the patient).
- Hormone therapy - cancers, such as prostate cancer need hormones to continue dividing. If the production of these hormones is inhibited, cancer growth can slow down.
Another cancer sensitive to hormones is breast cancer. Increasing levels of the hormone oestrogen are a major risk factor for the development and growth of breast cancer. This is because oestrogen binds to the oestrogen receptor, and the hormone-receptor complex can activate gene transcription in the nucleus. An example of a gene that the hormone-receptor complex can activate is growth factors that lead to uncontrollable cell division when produced in excess.
Cancer - Key takeaways
- Cancer is a disease in which cells grow uncontrollably to form tumours. These tumours can be benign or malignant.
- Benign tumours are non-cancerous as they are localised in one area, whereas malignant tumours metastasise and form secondary tumours.
- Cancer can be detected by laboratory tests, biopsies, and physical tests. They are treated in several ways depending on the type of cancer and the stage progression. Treatments include chemotherapy and radiation therapy.
- Examples of the types of cancers include prostate, skin and bowel cancers.
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