Newly-discovered human organ may help explain how cancer spreads

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The interstitium is fluid-filled compartments found just beneath the skin, and could rival our dermis for the biggest organ in the body.

"Initially, we were just thinking it's an interesting tissue, but when you actually delve into how people define organs, it sort of runs around one or two ideas: that it has a unitary structure or that it's a tissue with a unitary structure, or it's a tissue with a unitary function", said Dr. Neil Theise, professor of pathology at NYU Langone Health in NY, who was a co-senior author of the study.

What was once thought to be dense, connective tissues running all throughout the body has now been found to be a network of fluid-filled compartments that may act as 'shock absorbers'. The tissue contains interconnected, fluid-filled spaces that are supported by a lattice of thick collagen bundles, Theise said in the report.

Scientists have long known about the body's various interstitial spaces between cells, but its importance was never quite understood.

The study makes a good point that it's important to consider to what degree the microscopy techniques now in use reveal a true-to-life picture of what is happening in vivo, Radu Stan, a biologist at Dartmouth's Geisel School of Medicine who did not participate in the work, tells The Scientist.

The endoscopists, David Carr-Locke and Petros Benias of Mount Sinai Beth Israel, the acclaimed teaching hospital in NY, noticed a series of interconnected cavities that didn't match any known anatomy, according to the paper. The study also claims the interstitium is among the body's largest organs. While looking at the tissues around the bile duct and pancreatic ducts, they noticed a net-like structure surrounding fluid-filled spaces. Interstitial fluid is the source of lymph, which dispatches white blood cells, the body's immune system infection fighters, to wherever they're needed.

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"In describing this new layer of organised cells, the "interstitium", the researchers realised such tissue is the immediate route for cancer cells to leave their origin and migrate into the lymphatic vessels", he said.

This groundbreaking discovery will open up new research methods into cancer diagnosis and treatment.

The pockets of fluid are surrounded by a web of collagen interwoven by a flexible protein called elastin. But when the team examined live and freshly frozen bile ducts from 13 patients, there it was, an extended latticework of tissue.

Scientists had previously believe the tissue was a simple layer of connective tissue.

If the research is widely accepted the interstitium could be regarded as the body's 80th organ. The patterned tissue had dark, branching bands surrounding large, dye-filled polygonal spaces. Sure enough, they found that in some of the stomach and skin cancer tissue they looked at, cancer cells had spread into the interstitium. But scientists speculate that these useful properties could also work against us, allowing cancerous cells to spread throughout the body.

Theise and his colleagues are now investigating whether analysing the fluid in these newly-discovered channels might lead to earlier diagnosis of cancers.

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