Scientists discover a new organ: the interstitium

For decades, the space between the body's organs and tissues was classified as dense connective tissue — a kind of structural filler without its own relevant function. In 2018, researchers at New York University Langone Health published a study in Scientific Reports that reclassified these structures: they were not simple compact tissues but an interconnected network of fluid-filled cavities, supported by a framework of collagen fibres, that runs through virtually all the body's organs.

The term "interstitium" to describe these cavities was not new, but the proposal to classify it as an organ in its own right, with defined structure and function, generated debate in the scientific community. Advocates of the finding argue that the interstitial network has specific functional properties: it cushions organs against mechanical stress, participates in regulating the immune system and acts as a transport pathway for the fluid that eventually becomes lymph.

The hypothesis that captured the most public attention was the possible relationship with cancer spread. If cancer cells learn to travel through interstitial fluid, the network of cavities could explain some of the metastasis patterns that oncologists observe without a clear mechanism. Research on this front is still preliminary, but it opens a line of work that could have implications for both diagnosis and the design of therapies aimed at interrupting those dissemination pathways.