Cancer is a disease defined by the uncontrolled growth of abnormal cells, disrupting the body’s orderly process of cell creation and death. It begins when genetic changes allow cells to multiply without restraint. These altered cells can form masses of tissue known as tumors. While often thought of as a single condition, there are over 200 types of cancer that can arise in nearly any part of the body.
The Biology of Cancer
Every cancer begins with a disruption in a cell’s DNA. Genes within the DNA act as an instruction manual for cell growth and division. When mutations occur in these genes, the instructions can become corrupted, leading a cell to divide uncontrollably. As this cell multiplies, it passes its faulty genetic instructions to its descendants, creating a population of abnormal cells that can form a tumor.
These growths are categorized as either benign or malignant. Benign tumors are non-cancerous; while they can grow large, they do not spread to other parts of the body. Malignant tumors are cancerous, with cells that can invade nearby tissues and organs.
The defining feature of a malignant tumor is its capacity for metastasis. This is the process where cancer cells break away from the original, or primary, tumor. These cells can travel through the bloodstream or the lymphatic system. If they settle in a new area, such as the lungs or liver, they can establish a new, secondary tumor.
Major Classifications of Cancer
Cancers are classified based on the type of cell from which they originate. This origin determines the cancer’s behavior, growth rate, and treatment. The major classifications provide a framework for understanding this diversity.
The most common category is carcinoma, which arises from epithelial cells that form the skin and the linings of organs. Carcinomas that develop from epithelial cells producing mucus or other fluids are called adenocarcinomas. Breast, lung, prostate, and colon cancers are common examples.
Sarcomas are cancers that originate in the body’s connective and supportive tissues, including bones, muscles, cartilage, and fat. Sarcomas are much less common than carcinomas and are divided into bone sarcomas and soft tissue sarcomas.
Leukemias are cancers that begin in the blood-forming tissues of the bone marrow. This type of cancer does not form solid tumors but leads to the production of large numbers of abnormal white blood cells that crowd out normal blood cells.
Lymphomas and myelomas are cancers that arise from cells of the immune system. Lymphomas begin in immune cells called lymphocytes and often collect in lymph nodes. Myelomas start in another immune cell, the plasma cell, which is found in the bone marrow.
Known Causes and Risk Factors
While cancer is a genetic disease, only 5% to 10% of cases are linked to inherited mutations passed down through families. Most cancer-causing gene changes are acquired during a person’s lifetime due to environmental exposures and lifestyle choices.
Environmental factors include exposure to carcinogens, which are substances that can damage DNA. These include chemicals like asbestos and benzene, a component of gasoline. Physical agents, such as ultraviolet (UV) radiation from the sun or tanning beds, are a known cause of skin cancer.
Lifestyle choices are among the most impactful and modifiable risk factors. Tobacco use is the leading cause of preventable cancer deaths and is linked to cancers of the lung, mouth, throat, and bladder. Diet and physical activity are also strongly associated with cancer risk, as diets high in processed meats and low in fruits and vegetables can contribute to conditions like colorectal cancer.
Certain infectious agents can also increase the risk of developing cancer. For example, persistent infection with high-risk strains of human papillomavirus (HPV) is the primary cause of cervical cancer. The hepatitis B and C viruses can cause long-term liver infections that increase the risk of liver cancer. It’s important to understand that these factors increase risk; they do not guarantee that a person will develop cancer.
General Diagnostic Approaches
The process of diagnosing cancer involves detecting abnormal cells and determining their specific characteristics. Early detection through screening can improve outcomes. Screening involves tests on healthy individuals to check for disease before symptoms appear, such as mammograms for breast cancer and colonoscopies for colorectal cancer.
When a person has symptoms, a physician will begin with a physical exam and a review of their medical history. The doctor might feel for lumps or abnormalities. Blood and urine tests can also provide clues, as some cancers release substances called tumor markers into the bloodstream.
Imaging tests provide detailed pictures of the inside of the body. Computed tomography (CT) scans use X-rays to create cross-sectional images, while magnetic resonance imaging (MRI) uses magnets and radio waves for detailed images of soft tissues. A positron emission tomography (PET) scan involves injecting a radioactive substance that is absorbed by cancer cells, making them visible on the scan to help show if the cancer has spread.
A biopsy is almost always necessary for a definitive diagnosis. In this procedure, a small sample of suspicious tissue is removed from the body. A pathologist examines the tissue under a microscope to check for cancer cells and determine the cancer’s type and grade, which describes how likely it is to spread.
Foundational Treatment Strategies
The approach to treating cancer is tailored to the specific type and stage of the disease. The goal can be to cure the cancer, control its growth, or relieve symptoms to improve quality of life. Often, a combination of therapies is used to achieve the best outcome.
Surgery is the oldest form of cancer treatment and involves the physical removal of the tumor. It is most effective for solid tumors that are contained in one area. A surgeon may remove the cancerous tumor along with a small margin of surrounding healthy tissue.
Radiation therapy uses high-energy particles or waves, such as X-rays, to damage the DNA of cancer cells, which kills them or stops them from dividing. The radiation can be delivered from a machine outside the body or from radioactive material placed inside the body near the cancer cells. This treatment is localized to minimize damage to healthy tissues.
Chemotherapy is a systemic treatment that uses drugs to kill fast-growing cells throughout the body. Because cancer cells divide rapidly, they are more susceptible to these drugs. The medications travel through the bloodstream to reach cancer cells wherever they may be, making chemotherapy effective for cancers that have metastasized.
More recent approaches include targeted therapy and immunotherapy. Targeted therapy uses drugs designed to attack specific vulnerabilities in cancer cells. Immunotherapy works by boosting the body’s own immune system to recognize and destroy cancer cells more effectively.