What is cancer?

The human body is estimated to be composed of several trillions of cells with over 200 different cell types identified yet. Cancer is a disorder that results from the dysregulation of growth of any of them, meaning that cells replicate in an uncontrolled manner. Although there are protective mechanisms to prevent this from happening, an undetected mutation in a single cell might be enough to initiate cancer development - fortunately this is very rare, more often it is a multistep process referred to as “cancerogenesis”. The cell from which the cancer originates can be in theory any within your body, but this depends on an individual's genetics, the environment, lifestyle and cell types, as many of them are more resistant to damage than others and rarely divide. Therefore it is not just one disease, but a large group of disorders with various origins. 

The word “cancer” originated in ancient Greek, Hippocrates is said to have used the words “carcinos” and “carcinoma” due to the similarity in appearance of crabs and cancer lesions. Another word often used in the context of cancer is for example “oncology”, the study of cancer, which is derived from the old Greek word “oncos” translating to “swelling”.

“Cancer” is often used interchangeably with the word “malignancy”, referring to cell overgrowths (tumors) that invade tissue and spread through the body. In contrast to malignancies benign tumors are also overgrowths of cells, but they don’t invade adjacent tissue or spread and tend to cause only little troubles. Despite this, benign doesn't equal harmless, as even benign tumors can cause problems due to their local effects like e.g. compressing nearby structures.  

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What are cancer genes?

It’s a subset of more than 100 genes that are tightly associated with cancer. They contribute to the dysregulation of a healthy cell. Since these genes are associated with the abnormal growth of tissue, they are usually found in all cells of one tumor, supporting the thesis that they were present in the founding cell, which initiated the development in the beginning.

They have been distributed into groups according to their function:

• Oncogenes (promoting increased cell division, result from a mutation in a proto-oncogene, which are the physiological variants of these genes)
• Tumor suppressor genes (normally prevent abnormal growth of cells and induce cell death in case of damage)
• Genes regulating apoptosis (cell death) (promote cell survival)
• Genes regulating the interaction of tumor & healthy cells (inhibit the recognition of damaged cells by the immune system and therefore allow them to survive

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How does cancer develop?

There are many possible types of mutations affecting the genome (e.g. point mutations, gene rearrangements, deletions, gene amplification, translocations, …) of which some might even be inherited. If they are not detected by protective mechanisms and either corrected or the affected cell is not killed, they fall into one of two categories:

• driver mutations (pathogenic) - altering the function of cancer genes
• passenger mutations (neutral) - do not affect cellular behavior, anywhere in the genome

Passenger mutations may be initially harmless, but might contribute to selective advantages of the cell later.

Cancerogenesis or the development of cancer is fortunately in most cases a multistep process and more than a single mutation in a cell is needed to trigger uncontrolled cell growth. The process of tumor progression is simplified below.

Figure 1: The development of cancer 

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Throughout the development of cancer many subtypes of cells emerge and some might replicate or invade tissue easier than others giving them a selective advantage due to Darwinian selection. Treatment might further accelerate this process and complicate the therapy later, as only resistant cells survive. Therefore cancer tends to become more aggressive over time.

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What contributes to the development of mutations?

• Environmental factors (sunlight, asbestos exposure, occupational exposure to carcinogens, air pollution, infectious agents like viruses, chemicals, …)
• Lifestyle (diet, alcohol, smoking, exercise, obesity, reproductive history)
• Other diseases, esp. chronic inflammatory conditions (reflux esophagitis, hepatitis, inflammatory bowel diseases, …)
• Age
• Gender
• Genetics 

Some types of cancers are already well researched and definit causes have been identified, whereas the pathogenesis of others remains unknown or is assumed to be the result of a complex interaction between several factors. 

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What types of cancer exist?

Generally cancer is divided into blood (hematogenous) and solid tumors. 

• Hematogenous 

• Leukemia (immature white blood cells released into the blood)
• Lymphoma (from tissue of the lymphatic system)
• Myeloma (from cells in your bone marrow)

• Solid

• Carcinoma (from epithelial cells)

• from the lung, breast, prostate & other glands, GIT, skin, urinary system, …

• Sarcoma (from connective tissue cells)

• from bone, cartilage, muscle, blood vessels, adipose tissue, …

• Melanoma (from melanocytes in your skin, which are specialized neural cells)
• Germ cell tumors (testicular cancer, ovarian cancer, teratomas)
• Mixed tumors

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How does cancer spread?

In principle there are three ways how a tumor can spread from one location to the other.

1. Via blood (hematogenous) after invading a vessel or accidentally being introduced into it for example during surgery.
2. Via the lymphatic system, cells invade lymph vessels and are transported together with lymph to the next lymph node. Cells might replicate there and continue spreading to other lymph nodes or invade blood vessels.
3. A tumor might grow and invade nearby tissue directly. If the tumor spreads into a bodys cavity cells can also separate and fall onto other surfaces where they continue to grow. 

A tumor that has spread to another location is by definition malignant, those tumor “offsprings” are called metastases. Not every tumor spreads in the same way, sarcomas tend to spread via blood and carcinomas via the lymphatic system. Certain types of cancers even have a “favorite” or more common location of metastases. 

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How is cancer treated?

Cancer treatment is difficult and mostly performed by multidisciplinary teams. Over the last decade the treatment options and outcomes have improved greatly, therefore many types of cancers are nowadays treatable, but some remain virtually always lethal.

• Surgery is often necessary to remove a tumor. In early stages, before a cancer has spread, this might “cure” a patient, in later stages surgery might just be used to alleviate symptoms.
• Radiotherapy consists of using high energy radiation to destroy cancer cells. There are many forms of how the radiation can be delivered, ranging from highly precise techniques like the gamma knife, up to total body irradiation therapy.
• Chemotherapy describes the use of chemical agents that damage every cell in the body. Due to previous mutations cancer cells are less capable of recovering from this attack ultimately resulting in a reduction in the number of malignant cells. Because of its effects on the whole body, chemotherapy has many side effects and is nowadays often replaced by better, more targeted therapy approaches. It might also be used before or after surgery or radiotherapy to improve their results.
• Hormonal therapy is another type of systemic cancer treatment. It relies on the presence of certain receptors on the tumor cells which then can be blocked to reduce its growth.
• Targeted or biological therapy are newer forms of cancer treatments. In principle they try to maximize the effect on cancerous cells while minimizing any side effects. Receptors and other molecules found in cancer cells, but not healthy cells, are therefore targeted. 
• Immunotherapy is the newest form of cancer treatment. There are several approaches that ultimately make use of the body's own immune system to fight the cancer cells. These approaches range from using interferons up to retrieving and modifying T cells that then kill cancer cells. 

Combinations of several methods often achieve the best results, but the guidelines and evidence vary from type to type. 

Early diagnosis of cancer usually improves the outcome by a lot, which is why many countries established screening programs. Breast, prostate, skin and colorectal cancers belong among those that are often integrated in these programs, check your national guidelines or ask your doctor if you are eligible for any of those screening programs. 

Is there a way to prevent cancer from developing?

Besides an early diagnosis, there are ways to reduce the risk of cancer from developing in the first place. Harvard medical school has published an article (2019) regarding 10 ways to reduce your risk of developing cancer. 

• Stop smoking and avoid passive smoking. Be aware of your surroundings as kids are especially in danger of exposure to smoke without having the ability to avoid it.
• Stick to a healthy diet, you can find out more about a healthy diet in our article about the digestive system. 
• Exercise regularly, optimally more than three times per week for 30 minutes. Those 30 minutes don’t have to be in one piece, take breaks if you need them. 
• Maintain a healthy BMI (18 - 25) and take actions in case you are above/below it.
• Avoid consumption of alcohol and if you do drink, stick to recommended doses (≤2 drinks for men; ≤1 drink for women).
• Minimize your exposure to ionizing radiation (alpha -, beta-, gamma radiation, X-rays and UV light) and protect yourself in cases of unavoidable exposure. Wear protective clothing and apply sunblock regularly in summer. 
• Beware of environmental chemicals and possible contamination of your surroundings with e.g. asbestos, endocrine disruptors, benzens, PCBs, aromatic amines, etc. .
• Protect yourself from infections like HIV and HPV by using condoms and getting vaccinated (against HPV).
• Reduce your stress
• Consider vitamin D supplementation in case you can’t get the recommended amount of sun exposure. Vit. D is not a proven protective factor, but highly likely to contribute to the protection from cancer. 

As described before, chronic inflammatory states are associated with the development of cancer. Should you suffer from any condition like that, appropriate treatment is vital to improve your health and minimize the risk of developing cancer.