In Situ

The term in situ comes from the Latin and means “in the/its place.” In biology, the term usually refers to the study of an organism where it naturally occurs, such as in arid and desert conditions or at the bottom of deep ocean troughs, rather than how the organism reacts in a laboratory. In medical research, in situ research means studying the way people interact with their normal work or home environment to discover the potential sources of the various problems or disorders that may and do occur. This is particularly important when working out causes of problems based on occupational or residential factors, such as working in a place with regular exposure to radiation or living in a house that has major environmental problems such as dampness or pollution.

The study of problems in workplace environments has led to medical researchers developing the concept of occupational cancer, first developed by the British surgeon Sir Percivall Pott who, in 1775, made the discovery of the link between scrotal cancer in chimney sweeps with their regular exposure to soot.

The term in situ when used by oncologists usually refers to the study of malignant cancer cells in their location within a person rather than isolated on a petri dish or in a test tube. It can also be used to describe a carcinoma to refer to malignant cells that are present in the epithelium which have not been invaded beyond the basal lamina into deeper tissues. This is particularly important for developing techniques, including laser surgery. Bladder cancer at stage 0 is called a carcinoma in situ while it remains localized in the inner layer of the urinary bladder; however, as soon as it spreads, it is said to be no longer in situ. Similarly, while a stomach cancer carcinoma is only affecting the stomach, it is known as being in situ.

Geneticists have used the term in situ meaning “in the chromosome.” An example of this is “fluorescent in situ hybridization,” abbreviated as “FISH,” which can happen to chromosomes in cells when a target sequence is being observed.