Fundamentals of Cancer Detection, Treatment, and Prevention. Surya K. DeЧитать онлайн книгу.
DNA replication. Usually, these are tumor suppressor genes. If an error occurs in a DNA repair gene itself, however, its important correction function ceases, and errors in DNA copies can be mutations that might lead to cancer. Mutations in tumor suppressor genes (including BRCA1, BRCA2, and p53, which are all DNA repair genes) or oncogenes create the greatest likelihood of cancer occurring. Lynch syndrome is one of many genetic conditions originating from hereditary DNA repair gene mutations. Mutations of DNA repair genes can also be acquired.
Scientists know a lot about how cancer genes work. Many cancers, however, are not linked to one specific gene, but more likely result from multiple gene mutations. In addition, some studies suggest that genes interact with their environment, further complicating the current understanding of the role genes play in cancer. Each person's cancer has a unique combination of genetic changes, and as cancer develops, additional mutations occur. Even within same cancer, different cells may have different genetic alterations.
Given the earlier complexity, scientists continue to study how genetic changes affect cancer development. This information has led to improvements in cancer treatment, including early detection, risk reduction, the use of targeted therapy, and survival. Further research will provide additional understanding and a better overall outlook on the effects of this disease.
1.8 Tumors and Metastasis
As mentioned earlier, cancer starts when gene mutations interfere with the normal, orderly process of cell division. Cells begin to grow uncontrollably without stopping, sometimes forming a mass of tissue called a tumor. Tumors can be cancerous or benign. As previously mentioned, a cancerous tumor is malignant, meaning it can grow large and extend to other locations of the body. A benign tumor can become larger over a period of time, but will not spread to other parts of the body.
Metastasis is the medical term for cancer that appears in a different organ than where it originated from. When this occurs, scientists say the cancer has metastasized. Other terms referring to metastasis are metastatic cancer and stage 4 cancer. Some types of cancer do not form a tumor, including leukemias, most types of lymphoma, and myeloma.
One of the first places cancer often metastasizes to is the nearest lymph node(s). A lymph node is a tiny, bean‐shaped organ that functions in the human body's defense against infection. Lymph nodes are located in clusters in different parts of the body, such as the neck, groin area, and under the arms. Due to lymph nodes being part of a system, which circulates about the entire body, called the lymphatic system, cancer cells that reach the lymph nodes can be further transported to other body areas.
Metastases to the bones, brain, liver, lymph nodes, and lungs are very common. Some cancers tend to spread to certain parts of the body. For example, unresolved breast cancer spreads to the bones, liver, lungs, chest wall, and brain, whereas lung cancer tends to extend to the brain, bones, liver, and adrenal glands. Prostate cancer mainly spreads to the bones. Colon and rectal cancers have the greatest chance of spreading to the liver and lungs.
1.9 Hereditary Cancer Risk
In 5–10% of cancers, the major factor are gene mutations, which have been inherited and predispose an individual to developing the disease. Individuals with these inherited genetic mutations, or hereditary cancer syndrome, are at a significantly greater risk of developing associated cancer. The following conditions suggest a possible increased risk:
Family history of cancer: Having three or more relatives on the same side of the family with the same or related forms of cancer.
Cancer at an early age: Having two or more relatives diagnosed with cancer at an early age. This factor may differ depending on the type of cancer.
Multiple cancers: Having two or more types of cancer occurring in the same relative.
The possibility of heredity cancer is one reason why health screening questionnaires contain questions about cancer (and other illnesses) affecting extended family members.
Genetic Testing. If a person meets any of the criteria indicating they may have a heightened risk for developing cancer, an option they might wish to consider is genetic testing. Choosing to undergo genetic testing is a personal decision made for various reasons, but best made in collaboration with others, including other family members, one's physician, and a genetic counselor.
Currently, consideration of genetic testing is recommended in the following cases:
A personal or family history suggests a genetic cause of cancer.
A test will yield clear results regarding changes in a specific gene or genes.
The results will help with the diagnosis or management of a condition. This might guide someone at higher risk to counteract it with such steps as surgery, medication, frequent screening, or lifestyle changes.
Genetic counselors are very instrumental both in deciding whether or not to undergo genetic testing, as well as conferring with about the test findings. The counselor can explain the pros and cons of genetic testing, help people cope with the process of completing the testing, and give advice regarding ways to lower cancer risk in the future.
1.10 Cancer Screening and Diagnosis
Screening tests to aid physicians in the detection and diagnosis of cancer fall into one of four general types. Doctors conduct a physical examination to check for signs of any health abnormalities or indicators of disease, such as external lumps or localized pain. A thorough physical exam includes a review of the patient's family history of the disease, health history, and lifestyle factors, all of which may contribute to the development of cancer [15–36].
Laboratory tests, both routine and specialized, consist of an analysis of samples of tissue, blood, urine, or other bodily substances, to check for the presence of certain chemicals, abnormal cells, etc. A variety of imaging procedures are also available to give physicians a look at organs, bones, and other internal body structures. As mentioned earlier, genetic testing can provide information about specific gene mutations (changes) associated with certain types of cancer.
Before undergoing any screening tests, it is important to know the risks involved with the tests themselves, as some cancer screening tests pose more risk than the potential benefit. It should be ascertained whether the screening has actually been proven to reduce the chance of dying from cancer. Bleeding or other problems can result from certain types of screening procedures. For example, screening for colon cancer with sigmoidoscopy or colonoscopy can cause tears in the lining of the colon, leading to internal bleeding.
In addition, cancer screening test results may be abnormal even though there is no cancer present, which is called a false‐positive test result. A false‐positive result causes patient anxiety and usually follow‐up with more tests and procedures, which may have additional risks. On the other hand, test results sometimes indicate no cancer even though the disease is present. A person who receives a false‐negative test result may delay seeking medical care even if there are other abnormal symptoms.
Many screening tests have been shown to detect cancer at an early, more treatable stage and thereby reduce the risk of dying from this disease. The following is a list of a few types of cancer frequently encountered in modern societies, along with tests used to screen for them:
1.10.1 Colon Cancer
Colonoscopy, sigmoidoscopy, and high‐sensitivity fecal occult blood tests (FOBTs) have all been proven to decrease deaths from colorectal cancer. Colonoscopy and sigmoidoscopy also help prevent colorectal cancer because they detect abnormal colonic growths (polyps), which can be removed at that time before they develop into cancer. In addition, there are screenings for colon cancer in low‐risk patients using a stool sample, offering an alternative to the risks associated with, and the