Cancer

What is cancer?

Cancer is group of diseases that involves abnormal cell growth, where some of the body’s cells become abnormal and begins to divide too rapidly. Cancer can start almost anywhere in the human body, and many cancers can spread into surrounding tissue and/or travel to other parts of the body and form secondary cancers there.

Over a hundred different types of cancer have been diagnosed in humans. Previously, we used to sort cancer types based on where in the body they occurred or how the cancer cells looked in a microscope. Today, it is also common to characterize cancers based on the types of genetic alterations that are believed to be driving them. Researchers have found out that certain mutations commonly occur in many types of cancer, regardless of where in the body they first appear.

Different types of cancer

Cancer can affect various parts of the body and there are many types of cancer. Below is a list of some common and not-so-common types of cancer:

1. Breast Cancer
2. Lung Cancer
3. Prostate Cancer
4. Colorectal Cancer (includes Colon Cancer and Rectal Cancer)
5. Skin Cancer (including Melanoma, Basal Cell Carcinoma, and Squamous Cell Carcinoma)
6. Bladder Cancer
7. Kidney Cancer (Renal Cell Carcinoma)
8. Non-Hodgkin Lymphoma
9. Thyroid Cancer
10. Pancreatic Cancer
11. Leukemia (Cancer of the blood cells, including Acute Myeloid Leukemia, Acute Lymphoblastic Leukemia, Chronic Lymphocytic Leukemia, and Chronic Myeloid Leukemia)
12. Endometrial Cancer
13. Ovarian Cancer
14. Cervical Cancer
15. Testicular Cancer
16. Liver Cancer
17. Stomach Cancer (Gastric Cancer)
18. Esophageal Cancer
19. Oral Cancer (including cancer of the mouth and upper throat)
20. Nasopharyngeal Cancer
21. Laryngeal Cancer
22. Multiple Myeloma
23. Bone Cancer (including Osteosarcoma and Ewing Sarcoma)
24. Soft Tissue Sarcoma (Cancer of the muscles, tendons, and other soft tissues)
25. Brain Tumors (including Glioblastoma, Meningioma, and Acoustic Neuroma)
26. Hodgkin Lymphoma
27. Head and Neck Cancer
28. Oropharyngeal Cancer
29. Gallbladder Cancer
30. Bile Duct Cancer
31. Penile Cancer
32. Vaginal Cancer
33. Uterine Cancer
34. Mesothelioma (usually associated with exposure to asbestos)
35. Neuroblastoma (common in children)
36. Retinoblastoma (a childhood cancer that affects the retina of the eye)
37. Small Intestine Cancer
38. Pleural Mesothelioma
39. Thymoma and Thymic Carcinoma (cancers of the thymus gland)

This list is not exhaustive as there are numerous subtypes and rare forms of cancer. Additionally, the medical field continues to evolve with new classifications and understandings of cancer. It’s important to consult a medical professional for the most accurate and current information regarding cancer.

Do all cancers form solid tumours?

No, not all of them. Many types of cancer form solid tumours, which are masses of tissue. Some cancers, however, such as leukemia, are unlikely to form solid tumours.

Malign vs benign tumours

Cancer tumors are malign tumours and can both invade nearby tissue and spread throughout the body, as opposed to benign tumours which neither invade nor spread. Benign tumours can become large and can be dangerous in their own way (especially in the brain), but they behave very different from malign tumours.

Malign tumours can invade nearby tissue, and it is also possible for cancer cells to break off and be transported to distant parts of the body where they become the starting point for new tumours. Both the blood system and the lymph system are known pathways for cancer cells.

When a benign tumours is removed, it will usually not grow back. Malignant tumours are much more likely to grow back after being removed.

Cancer cells

Less specialization

One important difference between cancer cells and normal cells is that cancer cells are less specialized. Normal cells grow to fullfil a specific job in the body, e.g. being red blood cells or being a type of skin cells. Cancer cells work differently and they also continue to divide in an uncontrolled fashion.

Ignores commands

In the human body, normal cells eventually receive signals that tell them to stop dividing or begin apoptosis – a process of regulated cell death. They receive the signals and act accordingly. Cancer cells on the other hand ignore these signals.

Can tweak the microenvironment to their own benefit

In order to sustain the rapid cell division, cancer cells need plenty of oxygen and nutrients. Some cancers cells influence the normal cells around them to obtain these resources. A cancer tumour can for instance induce the creation of dedicated blood vessels that cater to the tumour, providing it with ample amounts of oxygen and nutrients, and removing the large amounts of waste products generated by fast-growing cancers.

Can evade the immune system

One important task for the immune system is to remove damaged and abnormal cells from the body, before they can cause harm and disruptions. Some cancer cells are able to hide from the immune system and keep from being removed. One of the ways that they do this is to take advantage of certain special immune system cells whose job it is to prevent a runaway immune response.

Genetics

Cancer cells appear when certain changes have happened to the genes that control the way our cells function – especially how they grow and divide.

In general, cancer cells feature more mutations than normal cells. It can sometimes be difficult to know what came first; are the mutations a driving force behind the cancer or have the mutations occurred as a result of the cancer. We do know that as the cancer continues to grow, additional changes do occur. Even within the same tumour, different cells can go through different genetic changes.

Environment

Research have found that cancer occurs both due to inherited factors and because of factors that the individual has been exposed to during their lifetime.

Examples of environmental factors that can cause damage to the DNA are radiation and certain chemicals in tobaccco smoke.

What are “the drivers of cancer”?

The genetic changes that contribute to cancer tend to impact three main types of genes:

• Proto-oncogenes, which are genes involved in normal cell growth. Mutations in a proto-oncogene may cause it to turn into an oncogene, which in turn can promote the growth of cancer cells because the changes allow cells to grow and survive when they should not.
• Tumor suppressor genes, which control cell growth and division.
• DNA repair genes, which are involved in fixing damaged DNA.

Changes in these three gene types are known as the drivers of cancer.

Metastasis

Metastasis is the development of secondary malignant growths at a distance from a primary site of cancer. It occurs when cancer cells break away from their original spot and travel to another part of the body. Cancer cells are known to use both the blood system and lymph system as “highways” for traveling. They then start growing in another part of the body, where they form metastatic cancer.

When observed under a microscope, the metastatic cancer cells usually look the same as cancer cells from the original cancer site. Studies on the molecular level typically reveal common molecular features as well, such as the presence of specific chromosome changes in both the original cancer and the metastatic cancer.

Tissue changes that can develop into cancer

Some types of non-cancerous tissue changes in the body should be monitored because they are known to sometimes develop into cancer.

Here are some examples of such changes:

• HyperplasiaThis is a condition where the cells within a certain tissue divide faster than the normal pace and extra cells build up. Hyperplasia can cause an organ to become extra-large. If we look at the tissue under a microscope, we see that the cells still look normal and that the tissue organization is the way it should be. Examples of common reason for hyperplasia are chronic inflammation, compensation for damage, and hormonal dysfunction.
• DysplasiaIn dysplasia, there is a build up of extra cells, the cells look abnormal under a microscope and the tissue is not organized correctly. It is a much more serious condition than hyperplasia. Generally speaking, a high degree of abnormality in the cells are linked to a high risk of cancer eventually developing.For some types of dysplasia, monitoring isn’t enough – the condition should be treated. An abnormal mole forming on the skin might, for instance, be removed surgically instead of being left there to develop.
• Carcinoma in situ is similar to cancer, but doesn’t fulfill the definition of cancer because the abnormal cells aren’t spreading to any other tissue. To prevent carcinoma in situ from developing into cancer, it is usually treated instead of just monitored.

This article was last updated on: July 4, 2023