Cancer is a complex disease characterized by unregulated cell division, leading to the formation of tumors. Tumors can be classified into two main types: benign and malignant. Benign tumors remain localized and do not invade surrounding tissues, while malignant tumors can spread to distant organs through a process known as metastasis.
There are three primary categories of cancer: carcinomas, leukemias/lymphomas, and sarcomas. Carcinomas, which arise from epithelial cells, account for the majority of cancer cases. Leukemias and lymphomas are cancers of the blood and immune system, respectively, while sarcomas, which originate in connective tissues, are much rarer.
The development of cancer is influenced by various factors, including carcinogens—substances that can cause cancer, such as tobacco, which is responsible for approximately 30% of all cancer cases. Epidemiology plays a crucial role in identifying these carcinogens by studying disease patterns within populations.
Cancer typically arises from DNA mutations, which accumulate over time. This process begins with tumor initiation, where genetic alterations lead to abnormal cell proliferation. As mutations accumulate, tumor progression occurs, allowing cells to divide uncontrollably and form tumors. The mutations often affect two types of genes: oncogenes and tumor suppressor genes. Oncogenes, when mutated, promote cell growth, while tumor suppressor genes normally inhibit cell growth. When these genes are altered, it can lead to cancer development.
Cancer cells exhibit several distinct characteristics. They are genetically unstable, accumulating mutations at a rapid rate. Unlike normal cells, which stop dividing when they come into contact with other cells (a phenomenon known as contact inhibition), cancer cells continue to proliferate, leading to tumor formation. Additionally, cancer cells can induce angiogenesis, the formation of new blood vessels, to supply nutrients and oxygen to the growing tumor. They also often have defects in apoptosis, the programmed cell death process, allowing them to survive and accumulate instead of dying off.
Understanding these fundamental concepts of cancer is essential for further exploration into its causes, types, and treatment options.