DESCRIPTION OF IN SITU

In biology, in situ means to examine the phenomenon exactly in place where it occurs (i.e. without moving it to some special medium).

In the case of observations or photographs of living animals, it means that the organism was observed (and photographed) in the wild, exactly as it was found and exactly where it was found. The organism had not been not moved to another (perhaps more convenient) location such as an aquarium.

This phrase in situ when used in laboratory science such as cell science can mean something intermediate between in vivo and in vitro. For example, examining a cell within a whole organ intact and under perfusion may be in situ investigation. This would not be in vivo as the donor is sacrificed before experimentation, but it would not be the same as working with the cell alone (a common scenario for in vitro experiments).

In vitro was among the first attempts to qualitatively and quantitatively analyze natural occurrences in the lab. Eventually, the limitation of in vitro experimentation was that they were not conducted in natural environments. To compensate for this problem, in vivo experimentation allowed testing to occur in the originate organism or environment. To bridge the dichotomy of benefits associated with both methodologies, in situ experimentation allowed the controlled aspects of in vitro to become coalesced with the natural environmental compositions of in vivo experimentation.

In conservation of genetic resources, "in situ conservation" (also "on-site conservation") is the process of protecting an endangered plant or animal species in its natural habitat, as opposed to ex situ conservation (also "off-site conservation").

In oncology: for a carcinoma, in situ means that malignant cells are present as a tumor but has not metastasized, or invaded, beyond the original site where the tumor was discovered. This can happen anywhere in the body, such as the skin, breast tissue, or lung. This type of tumor can often, depending on where it is located, be removed by surgery.

In medicine in-situ means that cancer cells have not passed through the basal lamina. Basically it means the tumor has not invaded lamina propria or the deeper portions of the tissue. Because metastasis generally requires a carcinoma to 'break through' the basement membrane, chances for metastasis is very low.