Cancer refers to any one of a large number of diseases characterized by the development of abnormal cells that divide uncontrollably and have the ability to infiltrate and destroy normal body tissue. Cancer often has the ability to spread throughout your body.
Cancer is the second-leading cause of death in the world. But survival rates are improving for many types of cancer, thanks to improvements in cancer screening, treatment and prevention.
Signs and symptoms caused by cancer will vary depending on what part of the body is affected.
Some general signs and symptoms associated with, but not specific to, cancer, include:
Fatigue
Lump or area of thickening that can be felt under the skin
Weight changes, including unintended loss or gain
Skin changes, such as yellowing, darkening or redness of the skin, sores that won't heal, or changes to existing moles
Changes in bowel or bladder habits
Persistent cough or trouble breathing
Difficulty swallowing
Hoarseness
Persistent indigestion or discomfort after eating
Persistent, unexplained muscle or joint pain
Persistent, unexplained fevers or night sweats
Unexplained bleeding or bruising
Make an appointment with your doctor if you have any persistent signs or symptoms that concern you.
If you don't have any signs or symptoms, but are worried about your risk of cancer, discuss your concerns with your doctor. Ask about which cancer screening tests and procedures are appropriate for you.
Cancer is caused by changes (mutations) to the DNA within cells. The DNA inside a cell is packaged into a large number of individual genes, each of which contains a set of instructions telling the cell what functions to perform, as well as how to grow and divide. Errors in the instructions can cause the cell to stop its normal function and may allow a cell to become cancerous.
A gene mutation can instruct a healthy cell to:
Allow rapid growth. A gene mutation can tell a cell to grow and divide more rapidly. This creates many new cells that all have that same mutation.
Fail to stop uncontrolled cell growth. Normal cells know when to stop growing so that you have just the right number of each type of cell. Cancer cells lose the controls (tumor suppressor genes) that tell them when to stop growing. A mutation in a tumor suppressor gene allows cancer cells to continue growing and accumulating.
Make mistakes when repairing DNA errors. DNA repair genes look for errors in a cell's DNA and make corrections. A mutation in a DNA repair gene may mean that other errors aren't corrected, leading cells to become cancerous.
These mutations are the most common ones found in cancer. But many other gene mutations can contribute to causing cancer.
Gene mutations can occur for several reasons, for instance:
Gene mutations you're born with. You may be born with a genetic mutation that you inherited from your parents. This type of mutation accounts for a small percentage of cancers.
Gene mutations that occur after birth. Most gene mutations occur after you're born and aren't inherited. A number of forces can cause gene mutations, such as smoking, radiation, viruses, cancer-causing chemicals (carcinogens), obesity, hormones, chronic inflammation and a lack of exercise.
Gene mutations occur frequently during normal cell growth. However, cells contain a mechanism that recognizes when a mistake occurs and repairs the mistake. Occasionally, a mistake is missed. This could cause a cell to become cancerous.
The gene mutations you're born with and those that you acquire throughout your life work together to cause cancer.
For instance, if you've inherited a genetic mutation that predisposes you to cancer, that doesn't mean you're certain to get cancer. Instead, you may need one or more other gene mutations to cause cancer. Your inherited gene mutation could make you more likely than other people to develop cancer when exposed to a certain cancer-causing substance.
It's not clear just how many mutations must accumulate for cancer to form. It's likely that this varies among cancer types.
While doctors have an idea of what may increase your risk of cancer, the majority of cancers occur in people who don't have any known risk factors. Factors known to increase your risk of cancer include:
Cancer can take decades to develop. That's why most people diagnosed with cancer are 65 or older. While it's more common in older adults, cancer isn't exclusively an adult disease — cancer can be diagnosed at any age.
Certain lifestyle choices are known to increase your risk of cancer. Smoking, drinking more than one drink a day for women and up to two drinks a day for men, excessive exposure to the sun or frequent blistering sunburns, being obese, and having unsafe sex can contribute to cancer.
You can change these habits to lower your risk of cancer — though some habits are easier to change than others.
Only a small portion of cancers are due to an inherited condition. If cancer is common in your family, it's possible that mutations are being passed from one generation to the next. You might be a candidate for genetic testing to see whether you have inherited mutations that might increase your risk of certain cancers. Keep in mind that having an inherited genetic mutation doesn't necessarily mean you'll get cancer.
Some chronic health conditions, such as ulcerative colitis, can markedly increase your risk of developing certain cancers. Talk to your doctor about your risk.
The environment around you may contain harmful chemicals that can increase your risk of cancer. Even if you don't smoke, you might inhale secondhand smoke if you go where people are smoking or if you live with someone who smokes. Chemicals in your home or workplace, such as asbestos and benzene, also are associated with an increased risk of cancer.
Cancer and its treatment can cause several complications, including:
Pain. Pain can be caused by cancer or by cancer treatment, though not all cancer is painful. Medications and other approaches can effectively treat cancer-related pain.
Fatigue. Fatigue in people with cancer has many causes, but it can often be managed. Fatigue associated with chemotherapy or radiation therapy treatments is common, but it's usually temporary.
Difficulty breathing. Cancer or cancer treatment may cause a feeling of being short of breath. Treatments may bring relief.
Nausea. Certain cancers and cancer treatments can cause nausea. Your doctor can sometimes predict if your treatment is likely to cause nausea. Medications and other treatments may help you prevent or decrease nausea.
Diarrhoea or constipation. Cancer and cancer treatment can affect your bowels and cause diarrhea or constipation.
Weight loss. Cancer and cancer treatment may cause weight loss. Cancer steals food from normal cells and deprives them of nutrients. This is often not affected by how many calories or what kind of food is eaten; it's difficult to treat. In most cases, using artificial nutrition through tubes into the stomach or vein does not help change the weight loss.
Chemical changes in your body. Cancer can upset the normal chemical balance in your body and increase your risk of serious complications. Signs and symptoms of chemical imbalances might include excessive thirst, frequent urination, constipation and confusion.
Brain and nervous system problems. Cancer can press on nearby nerves and cause pain and loss of function of one part of your body. Cancer that involves the brain can cause headaches and stroke-like signs and symptoms, such as weakness on one side of your body.
Unusual immune system reactions to cancer. In some cases the body's immune system may react to the presence of cancer by attacking healthy cells. Called paraneoplastic syndromes, these very rare reactions can lead to a variety of signs and symptoms, such as difficulty walking and seizures.
Cancer that spreads. As cancer advances, it may spread (metastasize) to other parts of the body. Where cancer spreads depends on the type of cancer.
Cancer that returns. Cancer survivors have a risk of cancer recurrence. Some cancers are more likely to recur than others. Ask your doctor about what you can do to reduce your risk of cancer recurrence. Your doctor may devise a follow-up care plan for you after treatment. This plan may include periodic scans and exams in the months and years after your treatment, to look for cancer recurrence.
The tumor (a mass of tissue of abnormal cells)or neoplasm formed by uncontrolled cell division can be of two types:
Benign tumors:
They are localized tumors and are bound within a connective tissue coating.
They don’t spread over the surrounding tissues.
They are not fatal or harmful. E.g. moles and warts
Malignant tumors:
They are cancerous and harmful and spread into the surrounding tissues by two means: invasion and metastasis.
Invasion is the penetration of the cells of malignant tumor into the neighboring tissue where they from invasion tumors.
Metastasis is the penetration of cancerous cell into the blood capillaries from where they are carried to different parts of the body.
Based on the types of tissues affected, cancer is of following types:
Carcinoma:
It is the cancer of the epithelial lining, which can be ectodermal, mesodermal or endodermal in origin.
This type of cancer can develop in the gut lining, glands (exocrine or endocrine) or skin etc.
About 80% of the cancers are carcinomas.
g. lung cancer, breast cancer, duodenal cancer, colon cancer, skin cancer, cervix cancer etc.
Sarcoma:
It is the cancer of connective tissues or muscles, and is mesodermal in origin.
Only 1-2% of cancers are of this type.
g. cancer of bones and cartilages etc.
Leukemia:
It is the cancer of blood particularly of granulocytes (WBCs) and hence is also called granulocytic leukemia.
It is a specific abnormality in chromosome 22 (Philadelphia chromosome) of leukemia cancer cells (particularly chronic myeloid leukemia (CML) cells).
Lymphoma:
It is the cancer of lymphatic tissues or lymphocytes present in the lymph.
The most common lymphoma is Hodgkin’s disease.
Mixed types of cancer:
Lipoma: it is the cancer of adipose tissue subcutaneous fats (beneath the skin).
Melanoma: the cancer of melanocytes present in skin.
Teratoma: it is the cancer of embryonic or fetal tissue that is a tumor-like embryo or embryo-like tumor formed by the heterogeneous mixture of tissues.
Myeloma: the cancer of bone marrow.
Myoma: the caner of muscles.
The cancer causing agents or factors are called carcinogens.
Carcinogens may be physical, chemical or biological factors.
Physical agents (Radiations):
UV rays, ϒ-rays (gamma rays), infra-red rays or X-rays can cause gene mutation and produce oncogenic transformation.
The radiation from nuclear bombs and leakage from nuclear reactors can also cause mutation.
Chemical agents:
Certain chemicals may cause cancer e.g. n-nitroso-dimethylene (in cigarette smoke) and asbestos dust causing lung cancer.
Cadmium oxide causing cancer of prostate gland, PVC (polyvinyl chloride) and Aflatoxin (from fungus Aspergillus) causing liver cancer.
Nitrosamine causing colon cancer, diethylstilbestrol causing vaginal cancer.
Biological agents (viruses):
Viruses don’t cause cancer as pathogens but alter DNA sequence which produces abnormal proteins.
Such viruses are called oncoviruses.
Carcinogens can also be categorized on the basis of their mode of action as:
DNA transformers: these agents can cause alteration in DNA that leads to cancer.
Tumor promoters: these agents (e.g. growth factors or hormones) promote the proliferation of cells which have already undergone genetic alteration.
Tumor viruses: such viruses are capable of making oncogenic transformations
Doctors have identified several ways to reduce your risk of cancer, such as:
Stop smoking. If you smoke, quit. If you don't smoke, don't start. Smoking is linked to several types of cancer — not just lung cancer. Stopping now will reduce your risk of cancer in the future.
Avoid excessive sun exposure. Harmful ultraviolet (UV) rays from the sun can increase your risk of skin cancer. Limit your sun exposure by staying in the shade, wearing protective clothing or applying sunscreen.
Eat a healthy diet. Choose a diet rich in fruits and vegetables. Select whole grains and lean proteins. Limit your intake of processed meats.
Exercise most days of the week. Regular exercise is linked to a lower risk of cancer. Aim for at least 30 minutes of exercise most days of the week. If you haven't been exercising regularly, start out slowly and work your way up to 30 minutes or longer.
Maintain a healthy weight. Being overweight or obese may increase your risk of cancer. Work to achieve and maintain a healthy weight through a combination of a healthy diet and regular exercise.
Drink alcohol in moderation, if you choose to drink. If you choose to drink alcohol, do so in moderation. For healthy adults, that means up to one drink a day for women and up to two drinks a day for men.
Schedule cancer screening exams. Talk to your doctor about what types of cancer screening exams are best for you based on your risk factors.
Ask your doctor about immunizations. Certain viruses increase your risk of cancer. Immunizations may help prevent those viruses, including hepatitis B, which increases the risk of liver cancer, and human papillomavirus (HPV), which increases the risk of cervical cancer and other cancers. Ask your doctor whether immunization against these viruses is appropriate for you.