photopheresis
noun
pho·to·phe·re·sis
| \ -fə-ˈrē-səs
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Medical Definition of photopheresis
: an immunomodulating therapy used especially to treat cutaneous T-cell lymphomas that involves treating blood with a photoactive drug (as methoxsalen), obtaining a fraction rich in white blood cells, exposing the fraction to damaging ultraviolet radiation, and returning it to the body where it stimulates a therapeutic immunological response