10.9:
Cancer
The general feature of cancer is uncontrolled cell division, which leads to a mass of cells called a tumor. A tumor is considered benign until it starts to invade nearby tissues, at which point it is then malignant.
In healthy cells, proliferation is tightly regulated through a complex network of positive and negative regulating factors. These factors make sure that cells divide only when they are supposed to. When genes encoding the positive regulators are mutated to produce over-active proteins, they are called oncogenes. Some viruses cause cancer through inserting their own copies of oncogenes into healthy cells. For example, the viral version of the SRC enzyme, a key molecule involved in cell signaling, is missing the regulatory domain that controls the human version. The lack of this domain triggers uncontrolled division in the host cells.
As opposed to oncogenes, tumor suppressor genes encode proteins that negatively regulate proliferation. When they are mutated, cell division proceeds unchecked. Up to 50% of human tumors have mutations in the tumor suppressor gene coding for p53. This multifunctional protein is essential for cell cycle control and apoptosis. Uncontrolled cell proliferation leads to tumor growth. This means that the cells need more oxygen and nutrients. In a process called angiogenesis, they produce growth factors that promote blood vessels to form in the tumor.
The more the tumor keeps growing, the more the cells keep dividing and changing, the higher the chance that cells can break free from the tumor and spread elsewhere in the body. The spread of cancer cells from the tumor is called metastasis, and is responsible for nearly 90% of cancer-related deaths. A major challenge to the treatment of cancer is the fact that it is not just one disease, each cancer patient has specific gene mutations, and every tumor is composed of a different group of mutated cells.
10.9:
Cancer
Cancers arise due to mutations in genes involved in the regulation of cell division, which leads to unrestricted cell proliferation. Modern science and medicine have made great strides in the understanding and treatment of cancer, including eradicating cancer in some patients. However, there is still no cure for cancer. This is largely due to the fact that cancer is a large group of many diseases.
Tumors may result in a case where two people have the same mutations in an oncogene or tumor suppressor gene. Initially, the tumors may be very similar. However, the uncontrolled cell division results in new random mutations. As the tumor cells continue to divide, they become more varied. As a result, the two tumors will grow at different rates and undergo angiogenesis and metastasis at different times. The two cancers become so distinct from one another that they will not respond in the same way to the same therapy. This demonstrates why even a particular type of cancer, breast cancer, for example, can be a myriad of different cancers, each disease case with its unique properties, potentially requiring unique treatment approaches.
As such, new cancer research and clinical trials focus on tailoring therapeutic approaches specifically for each patient’s genomic and molecular landscape. This is called personalized medicine. On the other hand, chemotherapy and other general treatments are also still needed and used successfully to treat many cancers. These approaches rely on the characteristic feature of all cancers: abnormal cell proliferation. Chemotherapy targets cell division processes, slowing down proliferation or killing fast-growing cells throughout the body. A different combination of cytotoxic drugs, chemicals that are toxic to cells, are used depending on the type and stage of the cancer.