Cancer is a population of cells (usually evolving from a single cell) that has lost its normal regulatory mechanisms and grows autonomously without being regulated. Cancer cells (malignant) can develop from any tissue in any organ. As cancer cells grow and multiply, they form masses of cancerous tissue – called tumors – that infiltrate and destroy normal adjacent tissue. The term “tumor” is associated with abnormal growths or masses. Tumors can be cancerous or non-cancerous, meaning that there are benign tumors and malignant tumors, and cancer is definitely malignant. Cancer cells coming from the primary (starting) site can spread (metastasize) to various parts of the body.
Development and spread of cancer
Cancer cells develop from normal cells through a complex process called transformation, the first step of which is “initiation”, where the cell’s genetic material (in the DNA molecules and in the structure called chromosomes) makes the cell cancerous. Changes in the cell’s genetic material can occur randomly or can be caused by substances that cause cancer (carcinogens). Carcinogens include many chemicals, tobacco, viruses, radiation, and sunlight. However, not all carcinogens have the same susceptibility. A genetic defect in a cell makes it more susceptible to cancer. Even chronic physical exposure can make cells more sensitive to carcinogens.
The second and last steps in cancer development are called “promoters” and the substances that cause them are called promoters. Promoters can be substances in the environment or drugs (such as barbiturates). Unlike carcinogens, agonists do not cause cancer themselves, but agonists make potentially stimulated cells cancerous (cancerous potential). There is no effect on cells that are not stimulated. Several factors are required to cause cancer, often a combination of susceptible cells and carcinogens.
Some carcinogens do not require a promoter to cause cancer, for example, ionizing radiation (X-rays, produced by nuclear power plants and atomic bomb explosions) can cause a wide variety of cancers, especially osteosarcoma, leukemia, thyroid cancer, and breast cancer.
Cancers can grow directly in the surrounding tissue and metastasize to other tissues or organs, adjacent or distant. Cancer can also spread in the lymphatic system. This type of metastasis is the typical way in which cancer metastasizes. For example, breast cancer first metastasizes to the adjacent lymph nodes and only after that does it metastasize widely throughout the body. Cancer can also spread with the bloodstream, and this type of spread is the typical form of sarcoma.
Types of cancer
Cancerous tissue (malignant) can be divided into blood and hematopoietic forms of tissue (leukemia and lymphoma) and “solid” tumors, often called cancers. Cancers can be sarcomas and carcinomas.
Leukemias and lymphomas are cancers of hematopoietic tissues, as opposed to forming masses, which can exist in the form of scattered cancer cells. In this way, they often crowd out normal cells in the bone marrow and blood stream. Thus, normal functioning cells are gradually replaced by cancer cells.
Carcinomas are epithelial cancers, these epithelial cells cover the surface of the organism and can produce hormones and form glands. Examples of cancer are skin cancer, lung cancer, stomach cancer, breast cancer, and prostate and colorectal cancers. Usually, cancer occurs more often in older people than in younger people.
Sarcomas are cancers of mesodermal cells, which form muscle and connective tissue. Examples of sarcomas, such as smooth muscle sarcoma and osteosarcoma. usually occur more frequently in older people than in younger people.
Risk factors for cancer development
There are many genetic and environmental factors that increase or decrease a patient’s risk of developing cancer.
Family history and genetic factors
Some families have a significantly higher risk of developing a particular cancer. Sometimes the increased risk is due to a single gene, and sometimes it is due to multiple genes interacting with each other. Environmental factors – for families – can alter this gene interaction and cause cancer.
An excess of abnormal chromosomes increases cancer risk. For example, in Down syndrome, patients have three chromosome 21s in place of the usual two, and they are at a high risk of developing acute leukemia from 12 to 20.
Age
Some cancers, such as nephroblastoma, retinoblastoma, and neuroblastoma occur almost exclusively in children. Why these cancers occur in children is unclear, but genetics is a factor. In the United States, 60 percent of cancers occur in people over the age of 65, and the risk of developing cancer doubles every five years after age 25. The increased cancer rate may be due to a combination of increased exposure time and odds to carcinogens and a weakening of the body’s immune mechanisms.
Environmental factors
Air pollution, from industrial waste or smoking can increase the risk of cancer. Smoking produces carcinogens, mainly causing the risk of lung, oral cavity, larynx, kidney and bladder cancers. Exposure to radiation is also a risk factor, and excessive exposure to ultraviolet light can cause skin cancer.
Geographical factors
Differences in the geographic distribution of cancer risk can be multifactorial; for example, genetics, diet, and environmental co-influences. For example, in Japan, the risk of bowel and breast cancer is low, while among Japanese who immigrated to the United States, the risk of developing the disease provides, ultimately, the same as the rest of the population in the United States. Conversely, Japanese have a fairly high incidence of stomach cancer, and when these Japanese move to the United States, their stomach cancer incidence drops to U.S. levels after one generation.
Diet
The foods eaten in the diet may increase the risk of cancer. For example, a high-fat diet is associated with an increase in colorectal cancer, breast cancer and possibly prostate cancer.
Viral infections
Several viruses are known to cause cancer in humans, and several are suspected to cause cancer. Papillomavirus is a cause of cervical cancer in women. Hepatitis B virus can cause liver in cancer.
Some viruses cause cancer in one country but not in others, e.g., E-B virus causes Burkitt’s lymphoma (a currently curable blood cancer) in Africa and nasopharyngeal cancer in China.
Inflammatory diseases
For example, ulcerative colitis can cause colon cancer; parasitic schistosome infection can cause bladder cancer through chronic inflammation.