in situ
Meaning of in situ: In situ describes something found or observed in its original, natural location, without having moved, spread, or been removed from that place.
Definition of in situ
In situ is a Latin phrase meaning in its original place, used in medicine to describe something observed or occurring exactly where it first formed, rather than having moved, spread, or been removed. The phrase is applied across several areas of medicine, from pathology to imaging, whenever location relative to the point of origin is the key detail.
The most familiar use is carcinoma in situ, a very early stage of cancer in which abnormal cells are confined to the layer of tissue where they first developed and have not invaded surrounding tissue or spread elsewhere in the body. This distinction affects both how the finding is classified and how it is approached.
The phrase can also describe other findings observed in their natural location, such as a device or structure examined without being removed or disturbed, in each case emphasizing that what is described has not moved from where it was found.
Used in a sentence
The biopsy report described the abnormal cells as carcinoma in situ, confined to the original tissue layer.
Good to know
Carcinoma in situ is distinguished from invasive cancer specifically by the absence of spread beyond the tissue layer where the abnormal cells first formed, a distinction that affects how the finding is classified.
Word origin
Where “in situ” comes from
From Latin in, meaning in, and situ, the ablative form of situs, meaning place or position.