Cancer is a complex group of diseases characterized by the uncontrolled growth and spread of abnormal cells within the body. Normally, cells grow, divide, and die in a regulated manner, but in cancer, this orderly process breaks down. This cellular malfunction can originate in almost any part of the human body. There are over 100 distinct types of cancer, each with unique behaviors and responses to treatment.
The Biology of Cancer Development
The human body constantly produces new cells through cell division. This process is tightly controlled by genetic instructions, ensuring cells multiply only when needed. Cancer development begins when these internal instructions within a cell’s DNA become damaged or altered, leading to genetic mutations. These changes disrupt the normal signals that regulate cell growth and division, causing cells to proliferate.
Genes that promote cell growth and division are called proto-oncogenes; when mutated, they become oncogenes, acting like an “always on” switch. Conversely, tumor suppressor genes slow down cell division or trigger cell death when there’s DNA damage. Mutations can inactivate these genes, removing the brakes on growth.
The accumulation of multiple genetic changes is required for a normal cell to transform into a cancer cell. These mutations can arise from errors during cell division, exposure to harmful environmental substances, or be inherited.
An abnormal mass formed from the uncontrolled proliferation of cells is called a tumor. Tumors are classified as either benign or malignant. A benign tumor is non-cancerous and remains confined to its original location, neither invading surrounding tissues nor spreading to distant body sites. These tumors grow slowly and have distinct borders.
In contrast, a malignant tumor is cancerous and can invade nearby healthy tissue. Malignant cells can break away from the primary tumor and spread to other parts of the body through the bloodstream or lymphatic system, a process known as metastasis. When cancer metastasizes, new tumors formed in distant sites still consist of cells from the original cancer, such as breast cancer spreading to the lung remains metastatic breast cancer.
Causes and Risk Factors
Cancer arises from various factors that can damage a cell’s DNA and disrupt its normal growth controls. Lifestyle choices play a role in cancer risk. Tobacco use is a leading cause of many cancers, including lung, esophageal, and oral cancers. Dietary habits and physical inactivity also increase the risk for several cancer types. Maintaining a healthy body weight reduces the risk, as excess fat cells produce hormones that can promote cancer growth.
Environmental factors contribute to cancer development through exposure to various carcinogens. Ultraviolet (UV) radiation from the sun is a cause of skin cancers, including melanoma. Exposure to certain chemicals, such as asbestos, can lead to cancers like mesothelioma. Other forms of radiation exposure also increase cancer risk.
Genetic factors account for a portion of cancers. While most cancer-causing mutations are acquired during a person’s lifetime, some cancers are linked to inherited genetic mutations. For instance, inherited mutations in genes like BRCA1 and BRCA2 are associated with an increased risk of breast and ovarian cancers. However, a genetic predisposition does not guarantee cancer development, and many individuals diagnosed with cancer have no known inherited risk factors.
Infectious agents are another category of risk factors. Certain viruses, such as Human Papillomavirus (HPV), cause cervical and other cancers, while hepatitis viruses increase the risk of liver cancer. The bacterium Helicobacter pylori is linked to an increased risk of stomach cancer. These agents can trigger chronic inflammation or directly alter cell DNA, contributing to cancer over time.
Categorizing Different Cancers
Cancers are named and classified based on the type of cell or tissue where they originate. This classification helps doctors understand the cancer’s likely behavior and guide treatment decisions. Carcinomas are the most common type of cancer, developing from epithelial cells that line the skin or the surfaces of internal organs and glands. Examples include lung cancer, breast cancer, colon cancer, and prostate cancer.
Sarcomas are less common cancers that arise in connective or supportive tissues. These include bone, muscle, fat, cartilage, and blood vessels. Examples are osteosarcoma (bone cancer) and rhabdomyosarcoma (muscle cell cancer).
Leukemia is a type of cancer that begins in blood-forming tissues, such as the bone marrow. It involves the uncontrolled production of abnormal white blood cells. Unlike carcinomas and sarcomas, leukemias do not form solid tumors but instead accumulate in the blood and bone marrow.
Lymphoma and Myeloma are cancers that originate in the cells of the immune system. Lymphoma affects lymphocytes, a type of white blood cell, and often starts in lymph glands or other parts of the lymphatic system. Myeloma is a cancer of plasma cells, found primarily in the bone marrow.
Detection and Diagnosis
Detecting cancer early improves treatment outcomes. Methods vary for screening versus diagnosis. Screening involves tests performed on healthy individuals to find cancer before symptoms appear, such as mammograms for breast cancer or colonoscopies for colorectal cancer. These proactive measures aim to identify precancerous changes or early-stage cancers when they are most treatable.
When a person experiences symptoms suggesting cancer, diagnostic tests are performed to confirm or rule out the disease. A physical exam is the first step, where a doctor checks for lumps or other abnormalities. Laboratory tests, including blood or urine tests, can detect tumor markers or other substances that indicate cancer, such as a prostate-specific antigen (PSA) test.
Imaging tests provide detailed pictures of the body’s internal structures. Common techniques include X-rays, useful for detecting bone tumors or lung abnormalities, and computed tomography (CT) scans, using X-rays to create cross-sectional images. Magnetic resonance imaging (MRI) uses strong magnets and radio waves to produce detailed images, particularly of soft tissues like the brain or spinal cord. Positron emission tomography (PET) scans involve injecting a small amount of radioactive material that cancer cells absorb more quickly, making them visible and assessing cancer spread.
Ultimately, the definitive diagnosis of cancer requires a biopsy. During a biopsy, a small sample of tissue or fluid is removed from the suspicious area. This sample is then examined under a microscope by a pathologist, who determines if cancer cells are present and identifies the specific type of cancer. This microscopic examination is important for confirming the diagnosis and guiding subsequent treatment decisions.
Principles of Cancer Treatment
The goals of cancer treatment are to achieve a cure, control the disease for as long as possible, or provide palliation by easing symptoms and improving quality of life. The choice of treatment depends on the type of cancer, its stage, and the patient’s overall health. Multiple treatment modalities are often combined.
Surgery involves physically removing the cancerous tumor and some surrounding healthy tissue. This approach is used when the cancer is localized and can be completely excised, making it a common treatment for many solid tumors. Surgery can also relieve symptoms caused by a tumor, even if a complete cure is not possible.
Radiation therapy uses high-energy rays, such as X-rays or electrons, to kill cancer cells or prevent their growth. This treatment can be delivered externally by a machine directing rays at the cancerous tissue, or internally by placing radioactive material near the cancer cells. Radiation therapy targets cancer cells by damaging their DNA.
Chemotherapy uses drugs that travel throughout the body to kill fast-growing cells, including cancer cells. These drugs interfere with cell division, affecting rapidly multiplying cancer cells more than most normal cells. Chemotherapy can be given orally or intravenously and is used to treat widespread cancer or to shrink tumors before surgery.
Immunotherapy helps the body’s own immune system fight cancer. These treatments boost the immune system’s ability to recognize and destroy cancer cells or remove signals that hide cancer cells from immune detection. Targeted therapy uses drugs designed to attack certain changes in cancer cells that allow them to grow. These therapies aim to minimize harm to healthy cells by focusing on unique features of cancer cells.
Hormone therapy is a treatment used for cancers sensitive to hormones, such as some breast and prostate cancers. This therapy works by blocking the body’s natural hormones or by preventing cancer cells from using them, slowing or stopping cancer growth.