Rates are increasing as more people live to an old age and as lifestyle changes occur in the developing world. The global total economic costs of cancer were estimated at US$1.16 trillion per year as of 2010. Etymology and definitions
The word comes from the ancient Greek καρκίνος, meaning crab and tumor. Greek physicians Hippocrates and Galen, among others, noted the similarity of crabs to some tumors with swollen veins. The word was introduced in English in the modern medical sense around 1600.Cancers comprise a large family of diseases that involve abnormal cell growth with the potential to invade or spread to other parts of the body. They form a subset of neoplasms. A neoplasm or tumor is a group of cells that have undergone unregulated growth and will often form a mass or lump, but may be distributed diffusely.All tumor cells show the six hallmarks of cancer. These characteristics are required to produce a malignant tumor. They include:
Cell growth and division absent the proper signals
Continuous growth and division even given contrary signals
Avoidance of programmed cell death
Limitless number of cell divisions
Promoting blood vessel construction
Invasion of tissue and formation of metastasesThe progression from normal cells to cells that can form a detectable mass to outright cancer involves multiple steps known as malignant progression. Signs and symptoms
When cancer begins, it produces no symptoms. Signs and symptoms appear as the mass grows or ulcerates. The findings that result depend on the cancers type and location. Few symptoms are specific. Many frequently occur in individuals who have other conditions.
These conditions are relatively uncommon.Conditions where the secondary polycythemia is not caused by physiologic adaptation, and occurs irrespective of body needs include:
Neoplasms – Renal cell carcinoma  or liver tumors, von Hippel-Lindau disease, and endocrine abnormalities including pheochromocytoma and adrenal adenoma with Cushings syndrome. People whose testosterone levels are high because of the use of anabolic steroids, including athletes who abuse steroids, or people on testosterone replacement for hypogonadism or transgender hormone replacement therapy, may develop secondary polycythemia. Blood doping - Secondary polycythemia can be induced by endurance athletes that take erythropoietin-stimulating agents, receive blood transfusions, and take other measures to increase their red blood cell mass in an effort to increase oxygen transport capacity. Altered oxygen sensing
Inherited mutations in three genes which all result in increased stability of hypoxia-inducible factors, leading to increased erythropoietin production, have been shown to cause erythrocytosis:
Chuvash erythrocytosis is an autosomal recessive form of erythrocytosis which is endemic in  patients from the Chuvash Republic in Russia. Chuvash erythrocytosis is associated with homozygosity for a C598T mutation in the von Hippel-Lindau gene (VHL), which is needed for the destruction of hypoxia-inducible factors in the presence of oxygen. Clusters of patients with Chuvash erythrocytosis have been found in other populations, such as on the Italian island of Ischia, located in the Bay of Naples. PHD2 erythrocytosis: Heterozygosity for loss-of-function mutations of the PHD2 gene are associated with autosomal dominant  erythrocytosis and increased hypoxia-inducible factors activity. HIF2α erythrocytosis: Gain-of-function mutations in HIF2α are associated with autosomal dominant erythrocytosis and pulmonary hypertension.