Cancer is a class of diseases in which abnormal cells divide without control and can invade other tissues. These cancerous tumors are capable of spreading throughout the body via the bloodstream or lymphatic system, thereby becoming more dangerous and difficult to treat as they grow. This uncontrolled growth may lead to death if the affected organ or tissue is not removed, or if cancer has metastasized.
There are many types of cancer, with the most common being breast, lung, and bowel cancers in women, prostate cancer in men, and lung, bowel, and stomach cancers in both sexes. Cancer affects all animals, but dogs and cats are less prone to most forms of the disease. In pets, cancer is far more common in older animals.
There are many different types of cancer, determined by what kind of cells cancer originates in and what causes its abnormal growth. Tumors may be benign (not likely to spread beyond their original site) or malignant (likely to invade neighboring tissue and begin growing at distant sites). Cancer that begins in one part of the body and then spreads to another is called metastatic cancer.
Cancer is also grouped into two main types of cells from which it originates: carcinomas and sarcomas. Carcinomas are cancers that originate in the skin or organs that line cavities inside the body, such as breast, prostate, colon, bladder, uterus, etc. Sarcomas are cancers that originate in bone, cartilage, fat, muscle, blood vessels, and other connective or supportive tissue.
Most types of cancer are carcinomas because these types of cells can invade surrounding tissues. This means that they can spread throughout the body via the lymphatic system or bloodstream.
Carcinomas are further classified based on what type of cells they originate in. For example, a skin cancer that originates in the epidermis (the outermost layer of skin) is called basal cell carcinoma.
Other examples of common types of carcinomas include:
The names of most types of carcinomas describe what cells they originate in, what part of that organ they affect, what tissue or structure surrounds that organ, what the tumor looks like under a microscope, what kind of cells it most closely resembles, what type of tissue or organ it may affect next, how quickly cancer spreads to other parts of the body, or what treatments are most effective.
For example, squamous cell carcinoma is a type of skin cancer that originates in flat cells called squamous cells and affects the epidermis.
This type of cancer closely resembles squamous cells, which are flat cells found on surfaces such as those lining the inside of the mouth and nose and moist areas between body parts.
Types of Sarcomas:
Anyone may develop cancer at any age, although the risk tends to increase as we get older. It is not caused by stress or lifestyle factors such as what we eat, how much we drink, what we smoke, or what we do during our free time. Having a strong immune system and avoiding excessive exposure to chemicals and radiation may help reduce the risk of developing cancer, as can maintaining a healthy weight and exercising regularly.
The symptoms of cancer vary greatly depending on what organ or what type of cancer is involved. Common symptoms of cancer include:
Other symptoms may also include fever, chills, night sweats, shortness of breath, cough, loose stools or constipation, back pain that does not go away with treatment or gets worse over time.
If an individual experiences any of these symptoms, they should talk to their doctor about getting a cancer screening. Cancer screenings help identify cancer early and improve treatment outcomes. They may be done by a family doctor or at a special clinic called a cancer center. Cancer screening tests may include blood tests, such as the breast self-examination test or a prostate-specific antigen (PSA) test.
Cancer is caused by abnormal cell division or mitosis. These cancerous cells can invade surrounding tissues and spread throughout the body via the lymphatic system or bloodstream. Once present in the bloodstream, they are then distributed to all parts of the body, where they infiltrate healthy tissue.
Each individual is born with a certain genetic susceptibility to cancer. In consequence, although everyone may develop the disease under the right conditions, those conditions vary from one person to another.
Cancer arises as a result of damage to DNA. DNA is what gives each cell its unique identity and function; without it, the cell would be unable to reproduce itself and would have no function. When a cell divides, its DNA is what gives each new daughter cell all the information it requires to take on the characteristics of its parent. If a piece of DNA is damaged either by an outside source or through a natural process called methylation, cells lose vital information. For example, if part of the DNA sequence that makes up a gene is damaged, the cell no longer manufactures vital proteins for proper function.
Where cancer has developed, DNA damage is present in virtually every cell. To survive and reproduce, healthy cells have something called a “repair kit”. This repair kit includes enzymes that can “fix” damaged DNA. However, cancer cells lack this repair kit and are unable to fix their genetic damage. Therefore, what distinguishes these cells from healthy ones is not the presence of cancer-specific genes (called oncogenes), but rather the loss of normal tumor suppressor genes. These tumor suppressor genes normally keep cell division under control and prevent damaged cells from multiplying.
After the loss of tumor suppressor genes, the cells are no longer governed by normal controls. They are free to divide and reproduce without limit unless specific agents intervene.
It is important to note what exactly distinguishes a cancer cell from its healthy counterparts. Most people believe that what makes a cancer cell different is the presence of oncogenes, which are what cause cancer. However, what distinguishes a cancer cell from a healthy cell is known as "epigenetics". Epigenetic proteins and enzymes control the activity of oncogenes and other genes in cells by marking DNA or histones (structures around which DNA is wound), causing certain genes to be expressed and others silenced. For example, these proteins may mark the DNA associated with tumor suppressor genes, leading them to be silenced or degraded by enzymes. These epigenetic changes are what distinguish cancer cells from healthy ones.
Over the recent years, there has been an increased interest in foods that may cause cancer. Some common questions surrounding this topic include what foods cause cancer? Does burnt food cause cancer? Some questions are even more specific towards the type of food and whether it is carcinogenic or not: is bacon a carcinogen? Do sausages cause cancer? Though these foods don't necessarily cause cancer themselves, some of them do increase the risk of getting cancer.
