Carcinogenesis requires that a single cell or one of its descendents undergo a s
ID: 74495 • Letter: C
Question
Carcinogenesis requires that a single cell or one of its descendents undergo a series of rare genetic and epigenetic changes that permanently alter the expression of at least five to eight genes. Thus, it is not surprising that many cancer cells assayed in cell culture dishes were found to have a very high rate of mutagenesis. (15 points)
A. What are three systems that are often defective in cancer cells whose role is to ensure the integrity of the genome?
B. The increased mutation rate speeds cancer progression by increasing the likelihood that a cell will acquire additional properties that contributes to carcinogenesis. Name four of the eight typical properties of cancer cells.
C. UV and ionizing radiation are known to cause cancer because they are mutagens that damage DNA. How, then, are the many anticancer therapies that act by damaging DNA, including ionizing radiation and many drugs, so effective at shrinking tumors?
Explanation / Answer
B. The increased mutation rate speeds cancer progression by increasing the likelihood that a cell will acquire additional properties that contributes to carcinogenesis. Name four of the eight typical properties of cancer cells.
Answer:
C. UV and ionizing radiation are known to cause cancer because they are mutagens that damage DNA. How, then, are the many anticancer therapies that act by damaging DNA, including ionizing radiation and many drugs, so effective at shrinking tumors?
Answer:
Chemotherapy is the treatment of cancer with one or more cytotoxic anti-neoplastic drugs (chemotherapeutic agents) as part of a standardized regimen. Traditional chemotherapeutic agents act by killing cells that divide rapidly, one of the main properties of most cancer cells. The efficacy of chemotherapy depends on the type of cancer and the stage. In combination with surgery, chemotherapy has proven useful in a number of different cancer types including: breast cancer, colorectal cancer, pancreatic cancer, osteogenic sarcoma, testicular cancer, ovarian cancer, and certain lung cancers.
Targeted therapy is a form of chemotherapy that targets specific molecular differences between cancer and normal cells. The first targeted therapies to be developed blocked the estrogen receptor molecule, inhibiting the growth of breast cancer. Another common example is the class of Bcr-Abl inhibitors, which are used to treat chronic myelogenous leukemia.
Radiation therapy involves the use of ionizing radiation in an attempt to either cure or improve the symptoms of cancer. It works by damaging the DNA of cancerous tissue leading to cellular death. To spare normal tissues (such as skin or organs, which radiation must pass through to treat the tumor), shaped radiation beams are aimed from several angles of exposure to intersect at the tumor, providing a much larger absorbed dose there than in the surrounding, healthy tissue. As with chemotherapy, different cancers respond differently to radiation therapy.
Radiation therapy is used in about half of all cases and the radiation can be from either internal sources in the form of brachytherapy or external radiation sources. The radiation is most commonly low energy x-rays for treating skin cancers while higher energy x-ray beams are used in the treatment of cancers within the body. Radiation is typically used in addition to surgery and or chemotherapy but for certain types of cancer, such as early head and neck cancer, may be used alone. For painful bone metastasis, it has been found to be effective in about 70% of people.