Men Lose the Y Chromosome From Their Cells as They Age. Arizona Cancer Researchers Scanned 4.3 Million Cell Nuclei From 405 Men Across 11 Organs and Found the Loss Is Highest in Tissue That Looks Normal but Sits Next to a Tumor, a Gradient 'Like a Hillside That Slowly Gets Steeper' Toward the Cancer.

Every cell in a man's body is supposed to carry one X and one Y chromosome. As men age, a growing share of their cells quietly drop the Y, a change geneticists call "loss of Y" that has been linked in blood cells to heart disease, Alzheimer's and higher death rates from cancer. A study from the University of Arizona Cancer Center now shows that the same loss shows up in solid tissue that looks perfectly healthy under a microscope, and that it gets worse the closer that tissue sits to a tumor.

The work, published in JCI Insight, was initiated by Dr. Dan Theodorescu, the physician-scientist who directs the Cancer Center and holds the Nancy C. and Craig M. Berge endowed chair. Rather than looking only at blood, his team systematically profiled Y chromosome loss across normal, precancerous and malignant tissue in 11 major human organs. Using an automated fluorescent imaging system, they analyzed 1,000 tissue samples from 405 men and inspected more than 4.3 million individual cell nuclei, measuring the ratio of Y to X chromosomes in each one.

"We were able to show that the loss of the Y chromosome is found in normal-appearing tissues adjacent to a tumor," Theodorescu said. "That finding is what makes this discovery so exciting. It suggests we may be looking at one of the earliest signposts of cancer forming." The researchers describe the phenomenon as a preneoplastic field effect: a hidden zone of genetic vulnerability in otherwise normal tissue that gives cancer fertile ground in which to start.

In one part of the study the team built detailed maps of bladder tissue removed during cancer surgery. Those maps let them watch Y loss climb from normal bladder lining, through early abnormal cells, into full-blown cancer. Across the organs studied, loss of Y in normal-appearing tissue was highest around cancers of the colon, rectum, esophagus, pancreas and lung, which together account for a large share of cancer deaths in men.

"We are now thinking of this as a gradient, similar to a hillside that slowly gets steeper," Theodorescu said. "The closer the tissue is to a cancer, the more Y chromosome loss we see. That gradient could one day help doctors suspect trouble in biopsies that miss a smaller cancer." That is the practical payoff the team is aiming for. A needle biopsy that lands a few millimeters from a small tumor can come back clean; a Y-chromosome readout on that same sample might tell a pathologist that something is growing nearby.

The finding builds on Theodorescu's earlier work showing that cancer cells which have lost the Y chromosome are better at hiding from the immune system, which helped explain why loss of Y has long been associated with worse survival from carcinomas. The new study pushes the story back a step, to before the cancer exists. It does not yet show that loss of Y causes tumors rather than accompanying them, and the authors do not claim it does. What it shows is that a genetic change once thought to be a harmless consequence of aging is concentrated exactly where cancer is about to happen, in tissue that every other test would call normal.