A diagnosis of cancer can be devastating. And there is good reason for this fear -- Cancer is the second leading cause of death in the United States next to heart disease, and will claim more than half a million lives this year.
The good news is that many forms of cancer can be avoided, and with early detection, a great number can be cured. In this article, we will look at the many faces of cancer so that you can understand the disease and its treatment, and also so that you learn about steps you can take to limit your exposure.
What we think of as "cancer" is actually a group of more than one hundred separate diseases. These diseases are all characterized by an abnormal and unregulated growth of cells. This growth destroys surrounding body tissues and may spread to other parts of the body in a process that is known as metastasis. You have probably heard of all of these different types of cancer:
There are many others as well.
Cancer can develop anywhere in the body, and at any age. Unlike infectious diseases such as AIDS, the flu (influenza), or tuberculosis, cancer is not contagious -- cancer is usually caused by genetic damage that happens inside an individual cell. Cells affected by cancer are called malignant cells. Malignant cells are different from normal cells in the body in that they divide (in most cases) much more rapidly than they should. This is important to know because many drugs used to fight cancer (antineoplastic or anticancer drugs) attack malignant cells during the active phase of cell division.
You may know someone who has had cancer, and his or her hair fell out during treatment. That happened because the anticancer drug(s) affected the normal hair follicle cells, which divide rapidly, as well as the rapidly-dividing malignant cells.
In the next section, we'll find out exactly what a tumor is.
When cells divide at an accelerated rate, they often begin to form a mass of tissue called a tumor. The tumor is fed by nutrients that diffuse through neighboring blood vessels and can also grow by forming a substance called tumor angiogenesis (vessel forming) factor. This factor stimulates the growth of an independent blood supply to the tumor.
Tumors can cause destruction in three common ways:
- Tumors put pressure on nearby tissues and/or organs.
- Tumors invade tissues and organs directly (direct extension), often damaging or disabling them in the process.
- Tumors make invaded tissues and/or organs susceptible to infection.
Tumors can also release substances that destroy tissues in close proximity to them.
One of the frightening things about cancer is the possibility of metastasis. This is the process where millions of malignant cells are released from the tumor (the primary) into the bloodstream. Fortunately, most of these cells are killed by trauma produced while traveling within the blood vessel walls, or by circulating cells from the immune system, like the Natural Killer (NK) cells and other T lymphocytes. Other immune cells that battle malignant cells are macrophages, antigen-presenting cells, and substances produced by immune cells called lymphokines. One common lymphokine is called interleukin-2 (IL-2) or interferon. (See How the Immune System Works for details on these different components of the immune system.)
In some cases, the circulating malignant cells survive and adhere to the inner muscular lining of the blood vessel walls. Here the process of tumor formation can begin in a different area of the body (the secondary), causing further destruction.
It is important to note that not all tumors are cancerous. Tumors can be either malignant or benign. A malignant tumor is cancer, and a benign tumor is not. One main difference between a benign tumor and a malignant tumor is that a benign tumor will not spread (metastasize) to distant parts of the body, and usually it will not grow back once removed. A benign tumor is either surgically removed, or it may be left in place and simply observed to see what it does. The decision to remove or observe depends on the tumor's size, type and location.
Next, we'll look at some of the causes of cancer.
Causes of Cancer
Cancer is caused by a number of factors, some of which we can control, and some we cannot. One of the uncontrollable factors is the presence of gene mutations. One type of gene that plays a role in normal cell growth -- an oncogene -- can be altered to contribute to the uncontrolled growth of a tumor. Oncogenes affect the way cells use energy and multiply. For example, in some cancers, the ras gene (an oncogene) is mutated, and produces a protein that stimulates cells to divide prematurely. Other oncogenes, such as C-myc and C-erb B-2, when amplified, are implicated in small cell lung cancer and breast cancer, respectively.
Mutations in tumor suppressor genes are another common cause of cancer. As you might expect, a tumor suppressor gene is supposed to prevent tumors. But when these genes are damaged, they can allow cancer to develop instead of preventing it. One of these genes, p53, normally prevents cells with abnormal DNA from surviving. When p53 is defective, these cells with abnormal DNA survive and can multiply, increasing the probability of developing cancer.
Certain cancers are associated with chromosomal abnormalities. Chromosomes are located within the nucleus of our cells, and contain our genes. When genes are missing, duplicated, or rearranged, a predisposition to develop a tumor is increased. Certain leukemias, sarcomas, lymphomas, and others tumors are associated with chromosomal abnormalities.
There are also viruses associated with cancer. The human papillomavirus (HPV) that causes genital warts is associated with carcinoma of the cervix, and the Epstein-Barr virus that causes infectious mononucleosis, is associated with Burkitt's lymphoma. Diseases or drugs that affect the immune system can also increase the risk for certain cancers. The disease AIDS, for instance, is associated with a high risk of two types of cancer, namely, Kaposi's sarcoma and lymphoma.
Exposure to ionizing radiation can increase the risk of certain cancers. X-rays used to treat disorders such as acne or adenoid enlargement can increase the risk of certain types of leukemias and lymphomas.
Fortunately, there are also factors under our control that can increase the risk of getting cancer, and can therefore be avoided. There are substances called carcinogens (cancer-forming agents) that can increase the risk of getting cancer. Some common carcinogens include:
- Arsenic, asbestos, and nickel, which can cause lung and other cancers
- Benzene, which can cause leukemia
- Formaldehyde, which can cause nasal and nasopharyngeal cancer
- and many others...
Carcinogens that are associated with a person's lifestyle include alcohol, which increases the risk of oral, esophageal, and oropharyngeal cancer, and tobacco, which causes lung, head and neck, esophageal, and bladder cancer. Smokeless or chewing tobacco can also increase the risk of oral cancer.
Unprotected exposure to sunlight (ultraviolet radiation) is associated with skin cancer. The main cancers caused by sunlight are basal cell carcinoma, squamous cell carcinoma and malignant melanoma.
We'll define some terminology that doctors use when they talk about cancer in the next section.
Have you ever wondered what in the world your doctor is talking about when he starts using big words to describe an illness or disease? Most of these words have Greek or Latin roots. Once you know the roots, you can more easily understand the words. I am going to give you a list of prefixes, suffixes and endings to help you understand what the doctor is saying when talking about different tumors.
Here is a list of common prefixes and their meanings:
- arthro- (joint)
- brachi- (arm)
- broncho- (windpipe)
- cardio- (heart)
- cephalo- (head)
- chole- (gall bladder)
- chondro- (cartilage)
- cranio- (skull)
- derm- or dermato- (skin)
- entero- (intestine)
- gastro- (stomach)
- gyno- (women)
- hemo-, hemato-, hemia- (blood)
- hepato- (liver)
- leuko- (white)
- myo- (muscle)
- neuro- (nerve)
- osteo (bone)
- stoma- (mouth)
The suffix -oma in terms such as fibroma or lipoma usually indicate a benign tumor.
The ending -carcinoma (as used in "squamous cell carcinoma") and the suffix -sarcoma (as used in "rhabdomyosarcoma") usually indicate a malignant tumor. The endings -lymphoma found in terms such as Burkitt's lymphoma and -leukemia found in chronic myelocytic leukemia also generally indicate a malignant process. So now when you hear a word like osteosarcoma, a malignant cancer of the bone, it is a bit easier to understand.
We'll find out how cancer is detected next.
Your doctor can help discover whether you have cancer by taking a detailed history, physical examination, imaging studies and laboratory tests. Your doctor will ask you questions about your general health, medications you may be taking, your family history, and your work history (environmental exposure to carcinogens, et cetera). You will be asked if you have any symptoms that may lead to a diagnosis of cancer, such as, fatigue, unexplained weight loss, night sweats, cough, blood found in vomit, urine or after bowel movements, and persistent pain. Inform your doctor if you have a painless ulcer in the mouth or on your skin that does not heal.
Your doctor will also do a complete physical examination, with special attention paid to the lymph nodes (in the neck, under the arms, et cetera), skin, lungs, breasts, genitals, and prostate (in men). Suspicious growths that may be potential tumors are often removed (using and excisional or incisional biopsy) or sampled (using a fine needle aspiration biopsy) and sent to a laboratory to be identified. A biopsy can also be obtained with the aid of a procedure known as endoscopy, where a tiny camera is used to view a suspicious lesion. Blood tests can help determine the extent or stage of certain cancers, and other abnormal findings correlated with different types of cancer. Imaging studies like X-rays, MRI, bone scans, or ultrasound can often determine the location and other characteristics of a tumor.
The American Cancer Society recommends screenings for certain types of cancer. Breast cancer should be tested for by self-examination every month for women over 18. Examination of the breasts by your doctor should be completed every three years for women between the ages of 18 and 40, then every year after age 40. A mammogram should be taken between the age of 35 and 40 as a baseline, then every 1 to 2 years between ages 40 to 49, and then annually after age 50. Women should also receive a Papanicolaou (Pap) smear to screen for cervical cancer annually between the ages of 18 and 65. An evaluation of the pelvis to screen for cervical, uterine, and ovarian cancer should be preformed every 1-3 years between the ages of 18-40, then annually.
For men, screening for prostate cancer should be completed yearly after age 50 (45 for high risk individuals), which includes rectal examination and a blood test for prostate specific antigen (PSA). Screening for rectal and colon cancer should be done with a rectal examination annually after age 40, with stool examination annually after age 50, and with sigmoidoscopy every 3 to 5 years after age 50.
In the next section, we'll look at cancer treatments.
Cancer is treated in a variety ways depending on the size of the tumor, its location, the type of cancer, and a host of other factors. Three common ways to treat cancer include:
- Chemotherapy (drug therapy)
In many cases, these methods are combined to get the most effective results. Let's look at each one in more detail.
Surgery is the oldest way to treat cancer. If the tumor is relatively localized, it can be surgically removed. Often, a border of healthy tissue surrounding the tumor is also taken to ensure that all of the malignant cells have been removed. Surgery is commonly used for cancer of the breast, colon, mouth, head and neck, kidney, testes and other parts of the body. Surgery can also be used to remove tissue that may become cancerous if left untreated (precancerous) and also to relieve symptoms caused by the cancer. Surgery is often combined with chemotherapy and/or radiation to improve results.
Radiation therapy, also know as radiotherapy, X-ray therapy, cobalt therapy, or irradiation, is useful in fighting cancer because it destroys cancer cells more easily than normal cells. Radiotherapy is commonly delivered with an external beam of x-rays, gamma rays or alpha and beta particles directed at the tumor. Radioactive pellets or wires can also be used internally if they are put in a tiny container and then implanted into the body near the tumor. In some cases, both internal and external radiation is used.
Radiation therapy is used for early Hodgkin's lymphoma, certain cancers of the lung, prostate, bladder, and other tumors. Radiation therapy is commonly used in conjunction with other therapies, including surgery and chemotherapy. For instance, radiation therapy may shrink a tumor to facilitate surgery, or be used as an adjunct after surgery to prevent the tumor from reforming. In some cases, radiation therapy is used alone, especially when the tumor is very susceptible to radiation, or when surgery to the area is too risky. Radiation can be used to shrink a tumor to provide relief from symptoms associated with tumor growth, even when a cure is highly unlikely.
Chemotherapy or drug therapy is used to kill cancer cells, while attempting to limit the damage to normal cells. Chemotherapy is useful in fighting cancer that has spread to other parts of the body and cannot be easily detected or treated with surgery or radiation therapy. Of the roughly 50 anticancer drugs, some can be used alone, or in combination with other anticancer drugs. Chemotherapy has been successful in treating acute leukemia, Hodgkin's and malignant lymphoma, small cell lung cancer, bladder and testicular cancer, and other forms of cancer. Chemotherapy can cure cancer in some cases, limit the spread of cancer, and help alleviate symptoms in some types of cancer. Chemotherapy can be used in combination with surgery and/or radiation, often with improved results.
Side effects from cancer treatment vary widely from person to person, and are also dependent on which type of therapy is used. Common side effects from chemotherapy include: nausea and vomiting, hair loss, fatigue, increased chance of bleeding or infection and anemia. Some potential side effects from radiation include, loss of appetite, skin changes and fatigue. Side effects from cancer surgery are similar to other types of surgery and include pain during recovery, temporary nausea from drugs used during anesthesia, and the potential for bleeding or infection after the surgery is completed. Your doctor and health care team are the best people to advise you about what side effects you can expect, and how to best manage them. There are medications, nutritional tips and other ways available to greatly reduce the impact of side effects from cancer treatment.
For lots more information about cancer and related topics, check out the links in the next section.