Oncology is the medical study and treatment of cancer, a class of diseases characterized by the unregulated division of cells. Cancerous cells can invade other tissues and spread throughout the body. This uncontrolled growth is the result of damage to cells’ DNA, causing mutations. These mutated, or abnormal cells, then multiply and grow to form cancerous masses called tumors. Cancerous cells can be caused by carcinogens, exposure to radioactive materials, or by some viruses. Mutations can also occur spontaneously, or may be passed down genetically.
Many types of cancer exist, and they can thrive in different areas of the body. Tumors are classified as either benign, meaning they do not invade surrounding tissues or travel (metastasize) to other parts of the body, or malignant, meaning they exhibit aggressive growth and invasiveness, including metastasis, and can be life-threatening.
Cancers are classified by the type of cell that resembles the tumor and, therefore, the tissue presumed to be the origin of the tumor. These are the general categories of cancers:
- Carcinoma: malignant tumors derived from epithelial cells. These are the most common cancers, including forms of breast, prostate, lung and colon cancer. They invade surrounding tissues and organs, and may spread to distant areas of the body by metastasis. There are several sub-classifications of carcinoma:
- Adenocarcinoma: A carcinoma originating in the epithelial cells of glandular tissue (glands) and forming glandular structures. This is a common type of lung, breast, colon, rectal and pancreatic cancer.
- Squamous cell carcinoma: Also a common lung cancer, this type of carcinoma develops from thin, flattened cells called squamous cells.
- Small cell carcinoma: Due almost entirely to smoking, they metastasize (spread) early. They are usually formed in the lungs, but can also be associated with other locations, such as the cervix. Small cell carcinoma is sometimes referred to as “oat cell carcinoma”.
- Large cell undifferentiated carcinoma: Aggressive and difficult to identify. It also tends to grow and spread quickly and widely.
- Lymphoma and Leukemia: Malignant tumors derived from blood and bone marrow cells. The cancer originates in lymphocytes, a type of white blood cell involved in the immune system. Because the lymphatic system is part of the body's immune system, patients with a weakened immune system, for example from an HIV infection or from certain drugs or medication, also have a higher occurrence of lymphoma.
- Sarcoma: Malignant tumors derived from connective tissue or mesenchymal cells. Sarcoma comes from the Greek word meaning “fleshy growth”, and affects connective or supportive tissues such as bone, cartilage, muscle, fat and blood vessels). Sarcomas account for less than one percent of all cancers, but its wide range of varieties and often subtle symptoms make diagnosis difficult.
- Glioma: A type of primary central nervous system tumor derived from glial cells. The brain is most commonly affected, although it can also strike the spinal cord, or any other part of the central nervous system, such as the optic nerves. Gliomas are named on the basis of the type of cell they specifically resemble. The main categories of gliomas are:
- Ependymomas: Tumors inside the skull, usually seen in children. They originate in ependymal (or glial) cells.
- Astrocytomas: Tumors inside the skull that are derived from brain cells called astrocytes. They are characterized by seizures or intense headaches.
- Oligodendrogliomas: A type of glioma derived from oligodendrocytes of the brain or from glial precursor cells. Primarily found in adults, and occurring mainly on the frontal lobe of the brain. Seizure activity is usually the first symptom, followed by headaches and increasing intracranial pressure.
- Mixed gliomas: These tumors contain cells from different types of glial cells.
- Mesothelioma: Tumors derived from the mesothelial cells in the protective linings of internal organs, especially the lungs, the abdominal cavity and the heart. This uncommon form of cancer is highly associated with asbestos exposure, and is aggravated by smoking.
- Germ cell tumors: Tumors derived from germ cells, normally found in the testicle and ovary. For females, these tumors are most often seen in young women or preteen and adolescent girls; for males, they generally occur after puberty. Germ cells can also travel to diverse areas of the body, such as the chest, abdomen and brain.
- Choriocarcinoma: Malignant tumors derived from the placenta — also characterized by early spread to the lungs.
Many forms of cancer are associated with exposure to certain environmental factors. These can include tobacco smoke (including second-hand smoke), radiation, alcohol, urban air pollution, diet, certain viruses, and ingestion of other carcinogens or contaminants such as coal dust, benzene or asbestos.
Many types of cancer may be preventable by changes in lifestyle behaviors and environmental interventions.
Diagnosing cancer usually requires a pathologist, although indications of cancer can be revealed through regular screenings or the appearance of symptoms. Three main groups of symptoms are recognized:
- Local symptoms: unusual lumps or swelling, pain or hemorrhage.
- Metastasis symptoms: enlarged lymph nodes, bone pain or cough.
- Systemic symptoms: poor appetite, weight loss, excessive sweating, anemia or excessive fatigue.
This is, of course, not a complete listing of possible symptoms, and a variety of conditions may cause any or all of the above symptoms.
When a cancer is suspected, a biopsy will usually be ordered by a pathologist. A biopsy is a sampling of tissue taken to be studied in a lab. Some can be performed in a doctor's office, while others require anesthesia and an operating room. The biopsy diagnosis will determine the type of multiplying cell and guide the doctor in recommending the best course of treatment.
Cancer screenings are performed to detect undiagnosed cancers and can lead to earlier identification. There are many different kinds of screenings, including breast self-examinations and mammograms for breast tumors, fecal occult blood testing and colonoscopy for colon cancer, Pap smears for cervical cancer, testicular self- examination for testicular cancer skin cancer screenings.
Grade: The term grade, when referring to a cancer, is a measure of how closely the malignant cells resemble normal cells when looked at under a microscope.
Choosing a Physician
When choosing a physician, you'll want to know that they are board-certified by the appropriate regulating body for their field. Board certification generally means that a physician has extensive experience, has passed rigorous testing, and has met higher professional qualifications.
Sub-specialties of medicine that typically work with cancer patients include surgical oncologists, medical oncologists and radiation oncologists. Medical City Fort Worth also offers orthopedic oncology Together, these specialists individualize the best treatment plan for each patient.