Cancer is a complex group of diseases characterized by the uncontrolled growth and spread of abnormal cells within the body. It arises when the body’s normal cellular processes malfunction, leading to cells that divide without regulation and can invade surrounding tissues.
Understanding Cancer
The human body is composed of trillions of cells, each with specific functions and a regulated life cycle. Normal cells receive signals that control their proliferation, ensuring new cells are produced only when needed to replace old or damaged ones. Cancer begins when these intricate controls break down, starting in a single cell or a small group of cells. Unlike healthy cells, cancer cells ignore growth signals, leading to uncontrolled multiplication. They often exhibit abnormal structures and lose their specialized functions, disrupting tissue organization. These cells originate from the body’s own cells but undergo transformations that allow them to behave abnormally.
How Cancer Forms and Spreads
The transformation of a normal cell into a cancer cell is a multi-step process driven by genetic mutations. These mutations are changes in the deoxyribonucleic acid (DNA) sequence, which contains instructions for cell behavior. Such changes can occur spontaneously during cell division, from environmental exposure, or be inherited. When these mutations affect specific genes, they disrupt the balance of cell growth and division.
For instance, mutations in proto-oncogenes can turn them into oncogenes, acting like accelerator pedals stuck in the “on” position, promoting continuous cell growth. Conversely, mutations in tumor suppressor genes, such as p53, disable the “brakes” that normally halt uncontrolled cell division or trigger cell self-destruction. Damage to DNA repair genes can also lead to an accumulation of further mutations, as the cell loses its ability to fix errors. It takes more than one gene mutation for a normal cell to become cancerous, often requiring a series of about six distinct changes.
As these abnormal cells multiply, they can form a mass of tissue called a primary tumor. If these cancerous cells acquire the ability to break away from the original tumor, they can spread to other parts of the body through metastasis. Cancer cells can enter the bloodstream or the lymphatic system. Once in these systems, they can travel to distant sites, such as bones, lungs, or the liver, and establish new tumors. These new metastatic tumors are composed of cells from the original cancer, retaining its characteristics rather than those of the new location.
Categories of Cancer
Cancers are broadly categorized based on the type of tissue or cell where they originate.
Carcinomas
These are the most common type, developing from epithelial cells that line internal organs and the outer surface of the body. Examples include lung, breast, and colon cancer.
Sarcomas
These are a less common group of cancers that form in connective tissues, such as bone, cartilage, fat, muscle, and blood vessels. Osteosarcoma, a bone cancer, is one example.
Leukemias
These are cancers of the blood-forming tissues, like the bone marrow, resulting in the overproduction of abnormal blood cells that do not form solid tumors.
Lymphomas
These originate in the cells of the immune system, specifically lymphocytes, which are part of the lymphatic system.
Factors Influencing Cancer Development
The development of cancer is influenced by inherited genetic predispositions and acquired risk factors from the environment and lifestyle. Approximately 5% to 10% of cancers are linked to inherited mutations, meaning a person is born with a genetic change that increases their susceptibility. For example, inherited mutations in genes like BRCA1 or BRCA2 significantly raise the risk for breast and ovarian cancers. Most cancers, however, arise from acquired mutations that accumulate over a person’s lifetime due to exposure to various carcinogens.
Lifestyle and Environmental Factors
Tobacco use, a major risk factor, introduces chemicals that damage DNA and promote mutations, contributing to cancers of the lung, mouth, and throat. Excessive alcohol consumption is linked to an increased risk of liver, breast, and colorectal cancers. An unhealthy diet lacking fruits and vegetables, and insufficient physical activity, also contribute to DNA damage and chronic inflammation, increasing cancer risk. Environmental exposures, including ultraviolet (UV) radiation from sunlight, can directly damage DNA and lead to skin cancers. Exposure to industrial chemicals like asbestos is associated with lung cancer and mesothelioma.
Infections
Certain infections, such as human papillomavirus (HPV) for cervical cancer and Hepatitis B or C for liver cancer, introduce foreign genetic material or cause chronic inflammation. This can lead to cellular changes and DNA damage, promoting cancer development. These factors can disrupt normal DNA repair mechanisms, allowing errors to persist and potentially lead to uncontrolled cell growth.
Identifying Cancer
Identifying cancer often begins with recognizing general changes in the body that could signal an underlying issue. These early warning signs are non-specific but warrant medical attention. They include unexplained weight loss, persistent fatigue, unusual lumps or swellings, and changes in bowel or bladder habits.
Screening Tests
Screening tests detect cancer in individuals without symptoms, aiming to find the disease at an earlier, more manageable stage. Examples include mammograms for breast cancer, colonoscopies for colorectal cancer, and Pap tests for cervical cancer. These tests can identify abnormal cell changes or early tumors before they cause noticeable problems.
Diagnostic Procedures
If a screening test or symptoms suggest cancer, diagnostic procedures confirm its presence and determine its type and extent. A biopsy, which involves taking a small tissue sample for microscopic examination, is the most definitive way to diagnose cancer. Imaging scans, such as X-rays, CT, MRI, and PET scans, provide detailed images of internal organs to locate tumors and assess their size and spread. Blood tests, including complete blood counts or tumor marker tests, can also reveal abnormalities that may indicate cancer. Early detection through awareness, screening, and diagnostic evaluation can significantly influence outcomes.