Any population of cells can grow in number by any one of three mechanisms including (i) shortening the length of the cell cycle, (ii) decreasing the rate of cell death and (iii) moving G0 cells into the cell cycle. All three mechanisms operate in normal and abnormal growth. In most tumors, all three mechanisms are important in determining the growth of the tumor, which is best characterized by its doubling time. Doubling time of tumors range from as little as 17 days for Ewing sarcoma to more than 600 days for certain adenocarcinomas of the colon and rectum. However, the fastest growing tumor is probably Burkitt’s lymphoma, with a mean doubling time of less than 3 days.
Cancer is a multi-step process in which multiple genetic alterations must occur, usually over a span of years, to have a cumulative effect on the control of cell differentiation, cell division and growth. Among human tumors, heritable mutations are an exception. Most alterations are acquired in somatic life in the form of chromosomal translocations, deletions, inversions, amplifications or point mutations. Certain oncogenic viruses play important roles in a few human tumors E.g., human papilloma-virus in cervical cancer and skin tumors.
The application of molecular biological techniques in the field of tumor virology, cytogenetic, and cell biology led to the discovery of the transforming genes of tumor viruses, the genes activated at the breakpoints of non-random chromosomal translocations of lymphomas and leukemia (Carlos and Harlan, 1994). Oncogene products are positive effectors of transformation. They impose their activity on the cell to elicit the transformed phenotype and can be considered positive regulators of growth. To the transformed cell, they represent a gain in function. Tumor suppressor gene products are negative growth regulators and their loss of function results in expression of the transformed phenotype.
The normally functioning cellular counterparts of the oncogenes, called proto-oncogene are also important regulators of biological processes. They are localized in different cell compartments, are expressed at different stages of the cell cycle, and appear to be involved in the cascade of events that maintain the ordered procession through the cell cycle.
In addition, the cell cycle is regulated by external mitogens (e.g. growth factors, peptide and steroid hormones, lymphokines), which activate a process called signal transduction by which specific signals are transmitted within the cell to the nucleus. The process is also mediated by non integral membrane associated proteins belonging to the tyrosine kinase, RAS gene families, and members of the MAPK family. Signals generated by mitogenic stimulation can lead to the expression of specific genes coding for proteins localized in the nucleus. Certain members of the nuclear oncogene protein family have been shown to be transactivators of specific RNA transcripts.
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Types of treatment in practice
Surgery is used to prevent, diagnose, stage, and treat cancer. Surgery can also relieve (palliate) discomfort or problems related to cancer. Sometimes, one surgery can take care of more than one of these goals. In other cases, different operations may be needed over time. Surgery can be explored to estimate the intensity of cancer. In most cases, the only way to know if a person has cancer and what kind of cancer it is by collecting a small piece of tissue and testing it. The diagnosis is made by looking at cells from the sample with a microscope or by doing other lab tests on it. The entire procedure is referred as biopsy. Another mode of surgery (staging surgery) is done to find out how much cancer there is and how far it has spread (Rungruang and Alexander, 2012). During this surgery, the area around the cancer including lymph nodes and nearby organs is examined. This is important because it provides information to guide treatment decisions and predict how people will respond to treatment. The curative or primary surgery is usually done when cancer is found in only one part of the body, and it’s likely that all of the cancer can be removed. In this case, surgery can be the main treatment. It may be used alone or along with other treatments like chemotherapy or radiation therapy, which can be given before or after the operation. Another type of surgery, debulking surgery is used to remove some, but not all, of the cancer for instance ovarian cancer (Schorge et al., 2010). It’s sometimes done when taking out the entire tumor would cause too much damage to nearby organs or tissues. For example, it may be used for advanced cancer of the ovary and some lymphomas. In these cases, the doctor may take out as much of the tumor as possible and then treat what’s left with radiation, chemotherapy, or other treatments. Palliative surgery is used to treat problems caused by advanced cancer (Gray and Adnan, 1997); correct a problem that’s causing discomfort or disability. For example, some cancers in the belly (abdomen) may grow large enough to block off (obstruct) the intestine. If this happens, surgery can be used to remove the blockage. Palliative surgery may also be used to treat pain when the pain is hard to control by other means (Hosoya and Lefor, 2011). Palliative surgery helps ease problems caused by cancer and helps people feel better, but it’s not done to treat or cure the cancer itself. Supportive surgery is done to help make it easier for people to get other types of treatment. For example, a vascular access device such as a Port-A-Cath® or Infusaport® is a thin, flexible tube that can be surgically placed into a large vein and connected to a small drum-like device that’s placed just under the skin. A needle is put into the drum of the port to give treatments and draw blood, instead of putting needles in the hands and arms each time.
Reconstructive surgery is used to improve the way a person looks after major cancer surgery. It’s also used to restore the function of an organ or body part after surgery. Examples include breast reconstruction after mastectomy or the use of tissue flaps, bone grafts, or prosthetic (metal or plastic) materials after surgery for head and neck cancers. Preventive or prophylactic surgery is done to remove body tissue that’s likely to become cancer-even though there are no signs of cancer at the time of the surgery. Sometimes an entire organ is removed when a person has a condition that puts them at very high risk for having cancer there. The surgery is done to reduce cancer risk and helps prevent the chance of cancer, but it doesn’t guarantee cancer prevention. For example, some women with a strong family history of breast cancer have an inherited change in a breast cancer gene (called BRCA1 or BRCA2). Because the risk of breast cancer is very high, removing the breasts (prophylactic mastectomy) may be considered. This means the breasts are removed before cancer is found. .
The advanced surgical techniques can also be utilized to facilitate the surgery of complex cases. The newer surgical techniques are less invasive, use different types of surgical instruments, and lead to less pain and shorter recovery times. Some of these techniques as shown below
o Laser surgery utilizing a beam of light energy
o Cryosurgery: Utilizes a liquid nitrogen spray or a very cold probe to freeze and kill abnormal cells. This technique is sometimes used to treat pre-cancerous conditions, like those affecting the skin, cervix, and penis. Cryosurgery can also be used to treat some cancers, like those in the liver and prostate. A scan (like an ultrasound or CT scan) might be used to guide the probe into the cancer and watch the cells freeze. This limits damage to nearby healthy tissue.
o Electrosurgery: A high-frequency electrical current can be used to destroy cells. This may be done for some cancers of the skin and mouth.
o Radiofrequency ablation: In radiofrequency, ablation, or RFA, high-energy radio waves are sent through a needle to heat and destroy cancer cells. RFA may be used to treat cancer tumors in the liver, lungs, kidney, and other organs.
o Mohs surgery: Mohs micrographic surgery is also called microscopically controlled surgery. It’s used to remove certain skin cancers by shaving off one very thin layer at a time. After each layer is removed, the doctor looks at the tissue with a microscope to check for cancer cells. This procedure is repeated until all the cells in a layer look normal. Mohs surgery is used when the extent of the cancer is not known or when as much healthy tissue as possible needs to be saved, such as when treating skin cancers near the eye.
o Chemosurgery is an older name for surgery like this and refers to certain drugs that may be put on the tissue before it’s removed. Mohs surgery does not use chemotherapy drugs.
o Laparoscopic surgery: A laparoscope is a long, thin, flexible tube that can be put through a small cut to look inside the body. It’s sometimes used to take pieces of tissue to check for cancer. In recent years, doctors have found that by making small holes and using special long, thin instruments, the laparoscope can be used without making a large cut. This can help reduce blood loss during surgery and pain afterward. It can also shorten hospital stays and allow people to heal faster. Laparoscopic surgery is used commonly today for many other operations. Laparoscopic surgery can be used in cancer treatment, but not for all cancers. Doctors can safely and effectively to use laparoscopic surgeries for some cancers of the colon, rectum, liver, prostate, uterus, and kidney.
o Thoracoscopic surgery: A thoracoscope is a thin tube with a tiny video camera on the end that can be put through a small cut into the chest after the lung is collapsed. This allows the doctor to see inside the chest. Tissue samples of any areas of concern on the lining of the chest wall can be taken out, fluid can be drained, and small tumors on the surface of the lung can be removed. This type of surgery leads to less cutting and has even been used to remove parts of the lung that contain cancer. Studies have shown that for early-stage lung cancer, results using this approach are much the same as removing part of the lung through a cut in the side of the chest.
o Robotic surgery: Robotic surgery is a type of laparoscopic (or thoracoscopic) surgery where the doctor sits at control panel and uses precise robotic arms to control the scope and other special instruments. The advantages of this type of surgery are largely the same as laparoscopic and thoracoscopic surgery: it can help reduce blood loss during surgery and pain afterward. It can also shorten hospital stays and let people to heal faster. Robotic surgery is sometimes used to treat cancers of the colon, prostate, and uterus. It has also been cleared for use by the FDA in operating on other body systems. It’s not yet clear if robotic surgery leads to better long-term results than operations where the surgeon holds the instruments directly.
o Other forms of surgery: Doctors are always looking for new ways to remove or destroy cancer cells. Some of these methods are blurring the line between what we commonly think of as surgery and other forms of treatment. Researchers are testing many new techniques, like using high-intensity focused ultrasound, microwaves, and even high-powered magnets to try to get rid of unwanted tissue. These techniques are promising, but still largely experimental. As doctors have learned how to better control the energy waves used in radiation therapy, some newer radiation techniques that work almost as well as surgery have been found. By using radiation sources from different angles, stereotactic radiation therapy delivers a large precise radiation dose to a small tumor area. The process is so exact that this is sometimes called stereotactic surgery, even though no cut is actually made. In fact, the machines used to deliver this treatment have names like Gamma Knife® and CyberKnife®, but no knife is involved. The brain is the most common site that can be treated using this technique, but it’s also used on some head, neck, lung, spine, and other tumors.
The term chemotherapy refers to the use of drugs to kill cancer cells. Usually, the drugs are given into a vein or they’re taken by mouth. Chemo drugs travel through the body in the bloodstream, reaching cancer cells that may have spread (metastasized) from the tumor to other places in the body. The chemotherapy is used to cure, control and palliation of cancer (Howie and Jeffrey, 2013). Either single or multiple drugs are indicated for cancer chemotherapy. Different drugs that work in different ways can work together to kill more cancer cells. This can also help lower the chance that the cancer may become resistant to any one chemo drug. Chemo may be used to shrink a tumor before surgery or radiation therapy. Chemo used in this way is called neoadjuvant therapy. It may be used after surgery or radiation therapy to help kill any remaining cancer cells. Chemo used in this way is called adjuvant therapy. It may be used with other treatments if your cancer comes back. However certain factors prevailing in the use of drugs that include the type of cancer, the stage of the cancer, the patient’s age, the patient’s overall health, other serious health problems (such as heart, liver, or kidney diseases) and types of cancer treatments given in the past. The chemotherapy is associated with diverse side effects that include, short-term side effects of chemo can include nausea and vomiting, loss of appetite, hair loss, and mouth sores. Because chemo can damage the blood-producing cells of the bone marrow, patients may have low blood cell counts. Low blood counts can cause certain side effects, such as higher risk of infection (from a shortage of white blood cells), serious bleeding or bruising after cuts or injuries (from a shortage of blood platelets), extreme tiredness or fatigue (sometimes from low red blood cell counts), cancer care teams carefully watch for and manage chemo side effects. Because everyone’s body is different, people notice different effects from chemo. Most chemo side effects go away after treatment ends. For instance, hair lost during treatment nearly always grows back after treatment. In the meantime, most patients are able to use wigs, scarves, or hats to cover, warm, or protect their heads.
3. Radiation therapy
The mode of therapy utilizes high-energy rays (like x-rays) to kill cancer cells and shrink tumors. The radiation may come from outside the body (external radiation) or from radioactive materials put right into the tumor (internal or implant radiation). Getting external radiation is much like getting an x-ray. The radiation itself is painless, but tissue damage may cause side effects. Radiation therapy is one of the most common treatments for cancer. It uses high-energy particles or waves, such as x-rays, gamma rays, electron beams, or protons, to destroy or damage cancer cells. Other names for radiation therapy are radiotherapy, irradiation, or x-ray therapy. Radiation can be given alone or used with other treatments, such as surgery or chemotherapy. In fact, certain drugs are known to be radio sensitizers. This means they can actually make the cancer cells more sensitive to radiation, which helps the radiation to better kill cancer cells. There are also different ways to give radiation. Sometimes a patient gets more than one type of radiation treatment for the same cancer. Radiation therapy uses special equipment to send high doses of radiation to the cancer cells. Most cells in the body grow and divide to form new cells. But, cancer cells grow and divide faster than many of the normal cells around them. Radiation works by making small breaks in the DNA inside cells. These breaks keep cancer cells from growing and dividing, and often cause them to die. Nearby normal cells can also be affected by radiation, but most recover and go back to working the way they should. Unlike chemotherapy, which exposes the whole body to cancer-fighting drugs, in most cases, radiation therapy is a local treatment. It’s aimed at and affects only the part of the body being treated. The goal of radiation treatment is to damage cancer cells, with as little harm as possible to nearby healthy cells. Some treatments use radioactive substances that are given in a vein or by mouth. In this case, the radiation does travel throughout the body. Still, for the most part, the radioactive substance collects in the area of the tumor, so there’s little effect on the rest of the body.
The long-term side effects of radiation therapy include, damage to victim’s body; radiation can damage to normal cells, and sometimes this damage can have long-term effects. For instance, radiation to the chest area may damage the lungs or heart. In some people this might affect a person’s ability to do things. Radiation to the abdomen (belly) or pelvis can lead to bladder, bowel, fertility, or sexual problems in some people. Radiation in certain areas can also lead to fluid build-up and swelling in parts of the body, a problem called lymphedema. A long-term problem linked to radiation treatment is the possible increased risk of getting a second cancer many years later. This is caused by the radiation damage to healthy tissues. The risk of this happening is small but real.
From the evidences, it can be understood that the link between radiation and cancer was noted many years ago in studies of atomic bomb survivors, workers exposed to radiation on their jobs, and patients treated with radiation therapy. For instance, young women who had radiation to the chest for the treatment of Hodgkin disease were later found to be at increased risk for breast cancer and some other cancers. Some cases of leukemia are also linked to past radiation exposure. The risk of leukemia increases within a few years of exposure, peaks about 5 to 9 years after the radiation, and then slowly declines.
Radiation treatments are much like x-rays and are not painful. The most common side effects are skin irritation and severe tiredness (fatigue). Fatigue is especially common when treatments go on for several weeks. It’s a feeling of extreme tiredness and low energy, which often does not get better with rest.
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