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Regression in 
*In
medicine
Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pr ...
is a characteristic of diseases to decrease in severity and/or size.
*Clinically, regression generally refers to lighter symptoms without completely disappearing. At a later point, symptoms may return. These symptoms are then called recidive.
*In cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
, regression refers to a specific decrease in the size or extent of a tumour. In histopathology, ''histological regression'' is one or more areas within a tumor in which neoplastic cells have disappeared or decreased in number. In melanomas, this means complete or partial disappearance from areas of the dermis (and occasionally from the epidermis), which have been replaced by fibrosis, accompanied by melanophages, new blood vessels, and a variable degree of inflammation.
References
Epidemiology {{disease-stub