Cancer Therapy, Definitive
Cancer Therapy, Definitive
Definitive cancer therapy is a treatment plan designed to potentially cure cancer using one or a combination of interventions including surgery, radiation, chemical agents, or biological therapies.
The primary purpose of definitive care is to establish a cure and to destruct and remove all cancer cells from the infected person.
Surgery is not only a diagnostic tool, but also used for tumor removal. The surgeon usually identifies potential candidates for tumor removal and repairs intraoperatively (during the operation procedure). Surgery can be curative for some stomach, genital/urinary, thyroid, breast, skin, and central nervous system cancers. The best chance for a surgical cure is usually with the first operation. It is essential that the cancer surgeon (oncologic surgeon) be experienced in the specific procedure.
Radiation therapy is commonly administered to approximately 50% of cancer patients during the course of illness. It can be used as the sole method of cure for tumors in the mouth and neighboring structures in the oral cavity, vagina, prostate, cervix, esophagus, Hodgkin's disease, and certain types of cancer in the spinal cord and brain. Research and clinical trials have demonstrated that combination treatment is more effective than radiation therapy alone.
Chemotherapy is curative for only a small percentage of cancers. It is most effective for choriocarcinoma, cancer of the testis, some types of lymphomas, and cancer of skeletal muscles.
Biological therapies are a new and promising direction for cancer cures. Usually when cancer cells grow they manage to derive a blood supply that allows passage of nutrients promoting continuation of abnormal cancer growth. Research that focuses on destroying these blood vessels is called angiogenesis. Cutting off the blood supply has been shown to destroy tumors, since this stops the flow of essential nutrients required for cancer growth. Use of certain growth factors also can stimulate self-destructive pathways in cancer cells (apoptosis). Gene therapy is directed toward inhibiting specific cellular signals that promote cancer cell multiplication. The importance of gene therapy in coming years will likely increase as scientists made progress in 2002 and 2003 are mapping the human genes (The Human Genome Project) and identifying new ways to fight and perhaps cure cancer. By using genetics, they hope to find new ways to activate human defenses against tumor cells and delay viral attacks on cells. Many trials were underway in 2003 that showed great promise. One of these in 2003 combined gene therapy and chemotherapy to stop breast cancer and its spread (metastasis).
Surgical resection requires an experienced surgeon, preoperative assessment, imaging studies, and delicate operative technique. Care should be taken during the procedure to avoid unnecessary tumor manipulation, which can cause cancer cells to infiltrate adjacent structures. If manipulation is excessive, cells can enter nearby areas for future re-growth. Accurate isolation of the tumor also can help avoid contamination of the surgical area. Early ligation of the blood supply to the tumor is an essential component of a surgical cure.
Radiation therapy requires extensive treatment planning and imaging. Care must be taken to localize the cancer field while attempting to spare destruction of normal tissue. This requires image monitoring and exact positioning during radiation treatment sessions.
Chemotherapy usually causes destruction of normal cells, and cancer cells can become immune to chemical destruction. Side effects and patient tolerance issues typically are anticipated and dosages may have to be specifically altered. Very few chemotherapeutic agents offer curative responses.
Biological therapies may cause patient toxicity resulting in extensive side effects. This can occur since the optimal dose may be exceedingly elevated above patient tolerance.
Surgical removal of the tumor must be performed with care and accuracy. The surgeon must avoid overmanipulation of the surgical field. Too much movement within the area can cause cancer cell displacement into surrounding tissue. If this occurs and no further treatment is indicated, the tumor may grow again. The surgeon also should perform an assessment concerning tissue removal around the cancer site. Tissue around the site may not by inspection seem cancerous, but adjacent structures may have cancer cells and surrounding tissue removal is usually part of the operative procedure. Pieces of tumor and the surrounding area are analyzed microscopically during the operation for cell type. An adequate resection (removal of tissue) will reveal normal cells in the specimens analyzed from areas bordering the cancerous growth. Surgery also can help to decrease the tumor bulk and, along with other treatment measures, may provide a cure for certain cancers. However, surgery is not always the best answer. It generally works best on slow-growing cancers.
Not only can surgery be curative for some cancers, but it is an essential diagnostic tool that must be assessed intraoperatively since microscopic analysis will guide the surgeon concerning tumor and surrounding tissue removal. These diagnostic procedures include an aspiration biopsy, which inserts a needle to extract (aspirate) fluid contained inside a cancerous growth; a needle biopsy uses a specialized needle to obtain a core tissue specimen; an incision biopsy removes a section from a large tumor; and an excision biopsy removes the entire tumor. The surgeon also can take samples of neighboring lymph nodes. Cancer in surrounding lymph nodes is an important avenue for distant spread of cancer to other areas. If microscopic analysis determines the presence of cancer cells in lymph nodes, the surgeon may decide to perform a more aggressive surgical approach.
Similar to surgical intervention, radiation therapy is a localized treatment. It involves the administration of ionizing radiation to a solid tumor location. This generates reactive oxygen molecules, causing the destruction of DNA in local cells. There are three commonly used radiation therapy beams: gamma rays from a linear accelerator machine produce a focused beam; orthovoltage rays are of less energy, thus penetrate less and typically deliver higher doses to superficial tissues (efficient for treating skin cancers); and megavoltage rays are high energy producing beams that can penetrate deeply situated internal organs, while sparing extensive skin damage. Two common routes can deliver radiation. Brachytherapy delivers radiation to a local area by placing radioactive materials within close proximity to the cancerous site. Teletherapy delivers radiation to a specific area using an external beam machine.
Curative chemotherapy usually requires multiple administrations of the chemical agent. Chemotherapy or systemic therapy is administered in the blood and circulates through the entire body. The choice of chemotherapeutic agents depends on the specific type of cancer. Chemotherapy is more commonly used for metastatic (malignant cancer which has spread to other areas beyond the primary site of cancer growth) disease, since very few cancers are cured by systemic therapy.
Biologic therapies primarily function to alter the patient's response to cancer. These treatments are mostly investigations and there are numerous research protocols studying the effects of biologic treatments. These protocols usually have strict admission criteria that may exclude potential candidates who can benefit from treatment. These treatments tend to stimulate specific immune cells or immune chemicals to destroy cancer cells.
For all treatment modalities imaging studies, biopsy, and constant blood analysis is essential before, during, and after treatments. Surgical candidates should undergo extensive pre-operative evaluation with imaging studies, blood chemistry analysis, stabilized health status, and readiness of staff for any potential complications and cell biopsy analysis. Patients with other pre-existing chronic disease may require intensive post-operative monitoring.
For radiotherapy, the patient undergoes extensive imaging studies. Additional planning strategies include beam localization to spare normal tissues, calibration of fractionated doses, and specific positioning during treatment sessions.
Patients who receive curative chemotherapy should be informed of possible side effects associated with the chemotherapeutic agent. Patients should also be informed of temporary lifestyle changes and medications that may offer some symptomatic relief.
Patients undergoing biologic therapies are usually advised of potential side effects, treatment cycles and specific tests for monitoring progress according to the specific research protocol.
Patients will typically be evaluated by imaging studies, blood analysis, physical examination, and health improvement. These follow-up visits usually occur at specific time intervals during the course of treatment. Surgical patients may require closer observation during the initial post-operative period to avoid potential complications. Reconstructive surgery can be considered to improve appearance and restore function. Certain surgical procedures (such as flaps and microsurgery of blood vessels) can restore new tissues to a previous surgery site.
Surgical therapy can be both disfiguring and disabling. Many normal tissues can be adversely affected by radiation therapy. Side effects that commonly occur shortly after a treatment cycle include nausea, vomiting, fatigue, loss of appetite, and bone marrow suppression (a decrease in the cells that provide defense against infections and those that carry oxygen to cells).
Radiation therapy also can cause difficulty swallowing, oral gum disease, and dry mouth. Additionally, radiation therapy can cause damage to local structures within the irradiated field.
Chemotherapy commonly causes bone marrow suppression. Additionally, cells called platelets—important for normal blood clotting—may be significantly lowered, causing patients to bleed. This may be problematic enough to limit the treatment course. Bone marrow suppression can increase susceptibility to infection and also cause infertility. Patients commonly have bouts of nausea and vomiting shortly after a treatment session. Rapidly multiplying normal cells also are affected such as skin cells (causing blistering and ulceration) and hair cells causing loss of hair, a condition called alopecia).
Bone marrow suppression — A decrease in cells responsible for providing immunity, carrying oxygen, and those responsible for normal blood clotting.
DNA — The molecule responsible for cell multiplication.
Titrate — To analyze the best end point (for dose) for a medication.
Biologic therapy risks
Biologic therapies can cause patients to develop suppression of cells that help the body fight against infection. Administration of certain chemicals that have anticancer effects can cause heart damage. Injection of killer immune cells (lymphokine-activated killer cells) may cause bone marrow suppression, and the host may reject the newly introduced cells.
Abeloff, Martin D., et al. Clinical Oncology. 2nd ed. Churchill Livingstone, Inc, 2000.
Goroll, Allan H., et al, editors. Primary Care Medicine. 4th ed. Lippincott, Williams & Wilkins, 2000.
"Gene Therapy and Chemotherapy Combine to Stop Breast Cancer and its Metastasis." Gene Therapy Weekly October 30, 2003: 2.
"Surgery Not Always Best Cancer Treatment Option: Weigh Advantages and Disadvantages Before Decision." Patient Education Management July 2003: 78.
Wachter, Kerri. "Gene Therapy Holds Promise for Curing Cancer: Four Preliminary Trials." Internal Medicine News September 15, 2003: 22.
American Cancer Society. http://www.cancer.org.
National Cancer Institute. http://cnetdb.nci.nih.gov/cancerlit.shtml..
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.