Tumor means an abnormal swelling in medicine so it includes any swelling that can occur as inflammation, cysts, hypertrophy, or hyperplasia, so it doesn’t only mean neoplasm. The definition of neoplasm is the De Novo growth, which is self-autonomous, continuous, and persistent although the stimulator is removed.
Neoplasm is formed of neoplastic cells (that contained abnormal nuclear DNA so they are genetically unstable) and stroma (that provides nutrition and support for the neoplastic cells). Neoplasms are classified according to the clinical behavior into Benign, Malignant (cancer), and intermediate behavior, while according to the histogenesis into epithelial and mesenchymal.
Most cancers fall into one of three main groups: carcinomas, sarcomas, leukemias, or lymphomas. Carcinomas, which include approximately 90% of human cancers, are malignancies of epithelial cells. Sarcomas, which are rare in humans, are tumors of connective tissues, such as muscle, bone, cartilage, and fibrous tissue.
Leukemias and lymphomas, which account for approximately 8% of human malignancies, arise from the blood-forming cells and from cells of the immune system, respectively.
Cancer growth upon the cell level occurs through many steps that persist consecutively, as there is mutation occurs upon the cells that have the capacity for proliferation, survival, invasion, and metastasis as the process falls initially into the genetic alteration which leads to abnormal proliferation of a single cell then the process progresses as an additional mutation that takes place within the cells of tumor population.
Causes of cancer are called carcinogenics that mainly lead to mutation induction as gene mutation is the initiator key for cancer development, DNA destruction, and cell proliferation. These causes may be radiation, chemicals, and viruses.