Cancer is an unregulated proliferation of cells. Its prominent properties are
A lack of cell differentiation
Local invasion of adjoining tissue
Metastasis, which is spread to distant sites through the bloodstream or the lymphatic system (often)
The immune system may play a role in eliminating early cancers or premalignant cells. This concept is termed immune surveillance. Patients with congenital or acquired immunodeficiency have an increased cancer risk, particularly those cancers associated with viral infection, kidney cancer, and melanoma.
Many cancers are potentially curable, particularly if detected at an early stage, and long-term remission is often possible in those detected at later stages. There is controversy whether cancers detected at an early stage, such as breast cancers detected by screening mammography or prostate cancers detected by screening prostate-specific antigen (PSA) testing, will progress during a patient's lifetime. However, for many cancers early detection increases the potential for cure.
When cure is not possible, as in many cases of advanced cancer, judicious treatment with surgery, chemotherapy, immune therapy, and/or radiation therapy may improve quality of life and prolong survival. However, in other patients, particularly in patients with poor functional status and in those with comorbid conditions, such treatment may be poorly tolerated, and palliative care may be appropriate.
