Final answer:
Carcinomas are cancers that originate in epithelial cells and include the majority of cancer types such as breast, lung, prostate, and colon cancer; amounting to about 90% of all cancer cases.
Step-by-step explanation:
Carcinomas are cancers of epithelial cells and account for 90% of all cancers. Cancers are broadly classified into several categories based on the type of cell that is initially affected. Carcinomas are derived from cells of the epithelium that cover the body surfaces and line cavities. These include cancers of the organs such as breast, prostate, lung, and colon cancer. Other forms of cancer, less common than carcinomas, include sarcomas (which affect connective tissues), lymphomas (which affect the lymphatic system), leukemias (which affect blood-forming cells), germ cell tumors, and blastic tumors.
Squamous cell carcinomas, for example, are a type of skin cancer affecting the squamous epithelial cells and can metastasize if untreated. A definitive diagnosis of cancer, including that of carcinomas, often requires a biopsy, where a sample of tissue is examined microscopically by a pathologist. This helps in not only confirming the presence of cancer but also in classifying its type, which is crucial for deciding treatment protocols.