Cancer is a group of diseases characterized by uncontrolled growth of cells in the human body and the ability of these cells to travel from the original site and spread to distant sites. Another name for cancer cells is malignant cells. Diet and nutrition play an important role in cancer prevention and cancer treatment.
By definition, cancer is a disease of the genes. A gene is a small part of DNA, which is the master molecule of the cell. Genes make proteins, which serve as the workhorses of the body’s cells. These proteins allow the body to carry out all of the many processes that permit breathing, thinking, moving, and others often taken for granted.
Throughout people’s lives, the cells in their bodies are growing, dividing, and replacing themselves. Many genes produce proteins that are involved in controlling the processes of cell growth and division. Any alteration, or mutation, to the DNA molecule can disrupt the genes and produce faulty proteins. This causes the cell to become abnormal and lose the restraints on its growth. The abnormal cell will begin to divide uncontrollably. The new growth it forms will be called a tumor or neoplasm. Not all tumors are cancerous. Those that are cancerous spread to other parts of the body near the original cancer site or to distant sites. Cancerous tumors are called malignancies. A tumor that is not cancerous is called benign.
Cancer can occur in anyone and is the second leading cause of death in the United States. Although cancer may be inherited, it also may occur due to certain environmental risk factors or behaviors. For example, it is well known that smoking can lead to lung cancer or that unprotected sun exposure is a risk factor for skin cancer. Diet and physical activity also play a role in cancer risk.
The American Cancer Society (ACS) estimated that almost one and one-half million new cases of cancer would be diagnosed in 2007 in the United States. And more than 1,500 people a day were projected to die of cancer in 2007. Lung cancer remains the leading cause of cancer deaths among U.S. men and women. Prostate cancer is the second-leading cause of cancer deaths among men and breast cancer is the second-leading cause of death among U.S. women. Colon and rectal cancer is the third-leading.
Most prevalent cancer-related deaths, 2002.
|Male cancers||Deaths||Female cancers||Deaths (000)|
cause of cancer death among U.S. men and women. There are various racial and ethnic differences in incidence of cancer and deaths from cancer in the United States. Some of these differences may be due to cultural factors such as behaviors or access to care. Others may be related to genetics. Survival rates for all races and types of cancer combined continue to increase substantially. From 1996-2002, 66% of cancer survivors lived five years or longer, combined with only 50% between 1975 and 1977.
Causes and symptoms
There are numerous risk factors and causes of cancer. Among them are age, sex, and family medical history. Some risk factors depend on the type of cancer. In some cases, a person may have more than one risk factor for the disease. Another person may be diagnosed with cancer and have no apparent risk factor. Genetic causes can’t be controlled by an individual, but people who know they are at risk because a close relative had a particular cancer should follow all recommendations for screening and prevention.
Often, physicians cannot explain what causes cancer. In addition to a family history of cancer, overall risk factors for cancer include aging, tobacco or alcohol use, exposure to sunlight or ionizing radiation, exposure to certain chemicals or substances, and exposure to some viruses and bacteria. Poor diet, lack of physical activity, or being overweight also are risk factors for cancers. Not all of these risk factors pertain to all cancers. For example, exposure to sunlight is a risk factor for skin cancer, while certain hormones increase the risk of breast cancer.
Cancer may not produce pain. And many symptoms may be due to a condition that is not cancer. But any signs similar to those for a particular cancer or that show a change in health should be checked by a physician. Symptoms vary depending on the type of. cancer, but some common symptoms of cancer include:
* feeling weak or very tired
* a lump in the breast or any other part of the body
* a new mole or changes in an existing mole
* changes to bowel or bladder habits
* hoarseness or a cough that won’t go away
* a sore that doesn’t heal
* difficulty swallowing
* unexplained weight loss or weight gain
* unusual discharge or bleeding
Generally, the earlier cancer is found, the better. Many cancer types have screening methods to help find them early. For example, screening mammography helps detect breast cancer before symptoms occur. A Pap test screens for cervical cancer. Several tests, such as colonoscopy, are recommended for people of certain ages or with certain risk factors, to screen for colon and rectal cancer. It is important to follow the guidelines of organizations such as the American Cancer Society concerning recommended screening for cancers.
Physicians use a combination of family and medical history, screening examination results, laboratory examinations, imaging examinations, and other procedures to diagnose cancer. Family and medical history are important to look for hereditary links to many cancers. Medical history helps to determine if a person may have behaviors, such as smoking, that increase risk for many cancers.
Laboratory examinations may test a person’s blood, urine, or other fluids. These tests often are conducted to search for levels of substances called tumor markers. Laboratory tests alone cannot diagnose cancer, but can help lead a physician toward or away from a suspected diagnosis.
X rays are traditional imaging and may be the first type of imaging performed. Mammography is a form of x ray; it is the screening and diagnostic examination used to detect breast cancer. Chest x rays may be used to detect lung cancer. Other types of x rays may be used in cancer diagnosis.
Computed tomography (CT) scanning. Because the use of the computer can generate finer, cross-sectional detail in combination with x rays, CT scans often are used to image a particular area. And CT scans have been used to screen for lung cancer, though the practice still is in debate. CT colonography can screen for polyps and other lesions in the large intestine, much like a colono-scopy. But CT is noninvasive, meaning it does not penetrate the skin or enter the body. CT may involve use of contrast that is injected to help make certain fluids or tissues more visible on the image for the radiologist.
Nuclear medicine or radionuclide scans involve injection of a small amount of a radiopharmaceutical into a vein. The agent flows through the bloodstream and collects in certain areas or organs. When a special camera is used to take images, the agent will show in “hot spots,” which the radiologist will use to interpret the results. Often, nuclear medicine scans will be used to check for spread of cancer to bone, but they also have other uses. Most of the radiopharmaceutical passes out of the body in urine or stool and the rest disappears through natural loss of radioactivity over time. Reaction to the agent is rare.
Ultrasound is an imaging examination that does not use radiation. Instead, high-frequency sound waves are used to produce images. Ultraound often is used to follow up in suspicious mammogram findings. Ultrasound images show fluids and soft tissues very well and often help radiologists determine if a mass is most likely a benign cyst or a malignant (cancerous) solid mass. Other common areas that ultrasound is used to image when diagnosing cancer are the thyroid, the abdomen, the pelvic area (ovaries, uterus), and the prostate.
Magnetic resonance imaging (MRI) also does not require use of radiation. Instead, a strong magnetic field and radio waves provide clear and detailed pictures through a computer display. MRI has proven to be the most sensitive examination for brain tumors. MRI also has become increasingly useful in breast cancer imaging in recent years, as well as for many other suspected cancers.
Positron emission tomography, or PET, scanning is a nuclear medicine procedure that acquires images based on detection of radiation, as in a radionuclide scan, but through emission of positrons. Positrons are tiny particles emitted from a radioactive substance administered to the patient. Cancer cells sometimes show up as areas of high activity. In recent years, physicians have been able to combine these images with CT images, fusing them with one another to show superb detail of the anatomy from CT scans along with the functional details gained from PET. These images improve diagnosis, staging, and tracking of treatment progress for cancer patients.
In most cases, at least for cancers that are solid tumors, a biopsy is the only definite method for confirming cancer diagnosis. Before many of the imaging methods discussed above were developed, a biopsy only could be performed through surgery, where a small sample of the tissue was cut out and sent to a laboratory for evaluation by a pathologist. Today, these samples can be extracted using small needles. The physician can be guided to the site of the suspected cancer by use of ultrasound, CT, MRI, or other imaging methods. The biopsy method often is called fine needle aspiration biopsy or core needle biopsy. Biopsies also may be performed during surgery, particularly to verify and stage cancer when a mass is removed as part of treatment. Removal and biopsy of the entire tumor is called excisional biopsy, while removal of only a portion of the tumor is called incisional biopsy.
Planning treatment for cancer first involves staging of the cancer. Once the physician has gathered the information needed to determine the cancer”s stage, the physician will communicate with the patient about treatment options. The most common treatments for cancer are chemotherapy, radiation, and surgery. A cancer patient may receive one or all of these treatments or a combination of them in any order. The particular use and details of each treatment depend on the type of cancer, the stage, and many other factors individual to each patient.
Cancer can spread, even early in the cancer cells” development. Chemotherapy uses cancer-killing drugs that are given to the patient by mouth or by intravenous injection. The drugs travel through the bloodstream to try to kill cancer cells throughout the body, not just at the original tumor site. Usually, the drugs are given in cycles and treatment can last up to six months. Chemotherapy may cause side effects, including fatigue, nausea, and increased susceptibility to colds and infections.
Also called radiotherapy or radiation treatment, radiation therapy usually is used to shrink or control growth of a tumor. The radiation destroys the cancer cells” ability to reproduce and the body naturally gets rid of the cells. In the past, radiation only came from external beam radiation therapy, where x-ray beams were directed toward the tumor from a machine outside the patient’s body. But patients also may receive brachy-therapy, a procedure in which radioactive sources, sometimes called seeds, are placed inside the body at the tumor site. Radiation therapy techniques have improved dramatically in recent years. Using computers and 3-D imaging, radiation oncologists and radiation therapists can precisely target the tumor area, sparing healthy tissues. Newer techniques even take into account natural movements such as breathing to better target the cancer cells. Radiation can produce some side effects, such as skin changes. Most of the effects are short term.
When a surgeon removes cancerous tissue, he or she often removes a little bit of the tissue around it. This is to ensure that all of the cancer cells were removed, to help minimize chance of recurrence. Surgery may require a hospital stay and recovery time, depending on the type and extent of the surgery. The belief that surgery for cancer leads to spreading of the disease is untrue.
Diet also is an important part of cancer treatment. It is important to eat the right kinds of foods before treatment, during treatment, and after treatment.
The American Cancer Society says that according to scientific evidence, about one-third of the cancer deaths that occur in the United States each year are due to nutrition and physical activity factors. These factors include excess weight. In 2006, the ACS recommended that Americans maintain a healthy weight throughout life, adopt a physically active lifestyle as adults and children, and consume a healthy diet with an emphasis on plant sources. The physical activity suggestions include at least 30 minutes of moderate to vigorous physical activity for adults five or more days a week, with 45 to 60 minutes of activity preferred. Children and adolescents should engage in at least 60 minutes of activity at least five days a week.
The ACS recommends choosing food and beverages that help to achieve and maintain a healthy weight. The society also recommends eating nine or more servings of a variety of fruits and vegetables per day. Whole grains should replace processed grains and the recommendations say to limit consumption of processed and red meats. Scientific evidence shows that populations with diets rich in vegetables and fruits but low in animal fat, meat, and calories have reduced risk of some common cancers.
Diet also is important during cancer treatment. Cancer and its treatment can cause nutritional deficiencies. Many cancer treatments can cause loss of appetite, and chemotherapy can additionally cause nausea. Radiation also can affect appetite, depending on the location of the tumor and treatment. Other nutritional needs for cancer patients arise because of a tendency to lose weight and muscle mass. When cancer is diagnosed, many patients will be placed on high-protein and high-calorie diets for a period of time to help maintain muscle and weight.
During treatment, the physician may recommend diet strategies to help soothe side effects. If patients are having trouble chewing or difficulty swallowing, thick liquids such as milkshakes may be suggested. Other semi-solid foods such as mashed potatoes may be helpful until swallowing or chewing ability improves. Other patients may have pain, nausea, vomiting, or diarrhea. Eating a meal before treatment may ease nausea. Eating small meals several times a day and choosing bland foods are some suggestions caregivers will offer patients to deal with nausea caused by cancer treatment. Diarrhea can be treated by eating broth, soups, sports drinks, or bananas and avoiding greasy foods. Loss of appetite can be overcome by eating small snacks that contain plenty of calories and protein and eating foods with odors that are appealing, as well as by trying new foods. Sometimes, cancer treatment alters the taste of foods. Rinsing the mouth before eating, using plastic utensils if foods taste metallic and adding spices to foods may help ease the symptoms.
After cancer treatment, it is important to resume healthy eating habits, following the recommendations of the American Cancer Society to maintain a healthy weight, be as physically active as possible, and to eat a balanced diet that leans toward whole grains and plant-based foods instead of red meats and processed foods.
Some cancer patients will need nutrition therapy to restore nutrients and remain nourished, particularly if they experience malnutrition because of their cancer or cancer treatment. Nutrition therapy may consist of enteral nutrition, also known as tube feeding. Enteral nutrition is food given in liquid form directly through a tube that is inserted into the stomach or small intestine. Parenteral nutrition is delivered into the blood stream through a thin tube, or catheter, inserted into a vein. Eating by mouth always is preferred to these methods, and patients are encouraged to eat as soon as they can following these nutrition therapies.
Some patients may receive palliative care for cancer. Palliative care is not treatment of the cancer, but steps taken to improve the patient’s quality of life and symptom side effects. Hospice is a program of special care for patients who are at the end of their life. It may be provided in a hospital, special hospice facility, or in cooperation with the patient’s family and other care-givers in the patient’s home.
Cancer prognosis depends on the type and stage of cancer at diagnosis, the person’s overall health at diagnosis, and treatment success. Studies show that physicians sometimes are reluctant to provide information about prognosis, so it is important for cancer patients to ask specific questions about their likelihood of survival if they want detailed information.
In addition to following the American Cancer Society guidelines concerning diet, nutrition, and activity, it is important to follow recommendations from the ACS, family physicians, and other credible health sources regarding behaviors that might lead to cancer. Examples of these behaviors include tobacco use and exposure to ultraviolet rays (sunshine) without protection. Anyone who has a first-degree relative with cancer should speak with their physician about their risk for the same type of cancer and participate in recommended screening as recommended. In cancer,early detection is essential to treatment and good prognosis.