What is cancer?: The basics

What is cancer?: The basics

Cancer is a disease that has affected human beings for thousands of years.

Although some forms of cancer are still very difficult to treat, nowadays, people with cancer are expected to live long lives at a much higher quality, even after being diagnosed, thanks to significant technological and medical advances in recent years.

Only in the last century did we really start to understand what cancer is and how it progresses. Since then, oncologists – doctors specialized in cancer – have made significant progress in terms of diagnosing, preventing and treating this disease.

Understanding what cancer is, why it forms and what causes it, as well as what treatments are available and how we can combat it, is still very complex.

Therefore, we have put together a basic guide for anyone who wants to know more about cancer.

This guide includes the following sections:

What is cancer?
Main forms of cancer
Most common types of cancer

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What is cancer?

To understand what cancer is, it is important to understand that inside our bodies, cells divide and grow at an controlled rate.

When does it all get out of control?

Cancer forms when several cells are altered and start to divide and grow at an uncontrollable rate, which leads to tumors.

Many cancers form tumors, however, not all tumors are malignant or cancerous, and it is important to know the difference to avoid any unnecessary worry.

This is the difference between a benign and malignant tumor:

Benign or non-cancerous tumor – does not invade other parts of the body and does not create new tumors

Malignant or cancerous tumor – displaces healthy cells, invades other tissues and organs and interferes with bodily functions.

Cancer keeps growing and expanding through direct extension or through a process called metastasis.

In metastasis, malignant cells travel through the lymphatic or blood vessels, and eventually form new tumors in other parts of the body.

Main forms of cancer

Many diseases come under the term “cancer” and can affect all parts of the body.

The main forms of cancer are:

  • Carcinoma

The most commonly diagnosed cancer which starts in the skin, lungs, breasts, pancreas and other organs and glands.

  • Sarcoma

Starts in the bones or in soft tissue (cartilage, fat, muscles, blood vessels, fibrous tissue…)

  • Melanoma

The most dangerous skin cancer which forms in the melanocytes responsible for producing the color of the skin.

  • Lymphoma

Develops in the lymphatic system responsible for protecting the organism against infections and diseases.

  • Leukemia

Type of blood cancer that starts in the bone marrow inside the bones, which affects the formation of blood cells.

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Most common types of cancer

There are more than 100 different types of cancer. Most cancers take the name of the organ or cells where they start; for example, cancer that starts in the colon is called colon cancer (1)
(1).National Cancer Institute, US National Institutes of Health. 

Although they share some similarities, different types of cancer grow and spread in different ways.

These are the most common types of cancer:

Breast cancer

Breast cancer, forms when the cells in the breast start to grow and an uncontrollable rate until they form malignant tumors that expand to other tissues.

Generally, these tumors can be observed in a mammogram or an ultrasound, or by feeling the lump or growth.

According to the World Health Organization (WHO), this is the most common cancer among women. Therefore, the American Cancer Society recommends all women over the age of 45 get a yearly mammogram (breast x-ray).

Lung cancer

This starts in the lungs and can spread to the lymph nodes or other organs in the body.

In general, lung cancer is grouped into two main categories: small cell and non-small cell, the latter being more common. Both develop in a different way and require different treatments.

Excessive smoking is the number one cause of lung cancers but non-smokers can also develop lung cancer.

Skin cancer

Forms in the skin tissue and is named after its location on the skin. Most skin cancer forms in the parts of the skin that are exposed to the sun, in people with a weak immune system. Find out more about this type of cancer here.

Colon cancer

Colon cancer develops in the large intestine (colon), which is the final part of the digestive tract.

It starts with a group of small, non-cancerous (benign) cells called an adenomatous polyp.

Over time, these polyps can turn into colon cancer; therefore, it is essential to maintain healthy eating habits (more on healthy eating below), to look after the body from the inside to protect it from illnesses.

Cervical cancer

Starts in the cells that cover the cervix, the lowest part of the uterus (matrix) that connects the uterus to the vagina.

Human papillomavirus (HPV) is linked to cervical cancer. Find out more about this type of cancer here

Prostate cancer

The prostate is the gland in the male body responsible for producing part of the liquid that makes up semen.

Prostate cancer forms when the prostate cells start to grow at an uncontrollable rate. It is recommended for men to be examined for this type of cancer from the age of 50.

Stomach cancer

Also known as gastric cancer or by its medical term, adenocarcinoma, stomach cancer starts in the cells that line the stomach and produce mucus.

In general, it starts with a stomach ulcer and symptoms such as heartburn, stomach pain, loss of appetite and weight loss.

If you think you have one or more of these symptoms, we recommend that you read our full guide on stomach cancer.

Thyroid cancer

Thyroid cancer has become increasingly common in recent years, and although its cause is still unknown, it has been linked to both environmental and genetic factors.

The thyroid is a gland located below the thyroid cartilage in the neck, known as the Adam’s apple, which is in the shape of a butterfly. Many different types of growths and tumors can develop in this gland. Most are not cancerous, but some are, and run the risk of spreading to nearby tissues and other parts of the body.

Pancreatic cancer

Consists of inflammation of the pancreas, a gland located below the stomach that is responsible for helping to digest food and hormones that regulate sugar.

See our full guide on pancreatic cancer, symptoms, diagnosis and treatments here.

Ovarian cancer

Ovarian cancer starts in the female reproductive organ, in one or both ovaries.

The spread of ovarian cancer is not easily detected, therefore, prevention and early detection play a fundamental role in its treatment. Do you know how to detect it? Read the full article here.

Testicular cancer

Testicular cancer is a complex type of cancer that can affect men at any age. It is more common in men between the ages of 20 and 34, but in reality it is relatively rare.

Testicular cancer starts in the germ cells (cells that produce sperm), and can be cured with timely treatment, even if they are diagnosed in the later stages.

Liver cancer

The liver is the second largest organ in the body, which is responsible for filtering the blood and creating enzymes that help the body digest food, among other functions.

The signs of liver cancer are often silent in the initial stages, as symptoms start to appear as the tumor grows, for example, experiencing pain in the upper part of the abdomen, which sometimes extends to the back.

Bone cancer

Bone cancer is not common and includes various types; some forms of bone cancer, such as osteosarcoma and Ewing’s sarcoma, are more common among children and young adults.

Kidney cancer

Also known as renal cancer, it can affect adults as well as children. Certain genetic conditions increase the risk of developing this disease, therefore it is better to have regular check ups to avoid any unwanted surprises.

The main types of kidney cancer are: renal cancer, transition cell cancer and tumor diseases that you can read more about in our specialized article.

Mouth and throat cancer

This type of cancer falls into the category of head and neck cancers, which includes the larynx, throat, nose and tongue, among others.

Some risk factors that increase the chances of developing this type of cancer are excessive alcohol or tobacco consumption and human papillomavirus (HPV).

Find out more about this type of cancer here.

Tongue cancer

Over 90% of oral and oropharyngeal cancers are squamous cell carcinomas, meaning that they start in the flat and squamous cells that are found on the tongue lining.

Fortunately, early detection and treatment are relatively straightforward for this type of cancer. For more information, click here.

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