In medical language, PR most often means per rectum, which refers to giving medicine, doing an exam, or taking a temperature by the rectal route. In cancer care, PR can also mean partial response, which under RECIST criteria means tumor lesions have decreased by at least 30% from baseline without new lesions or progression of existing ones. That's why this abbreviation causes so much confusion. A person might see PR on a prescription, a hospital note, a pathology report, or an oncology update and assume it has one fixed meaning. It doesn't. The meaning depends on where it appears, what
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