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Cancer patients rare die directly from their tumors. Anyone who’s lost a friend or loved one knows the disease usually wastes away the body. Often, at the end stages, food just doesn’t seem to stick.

Now a new study may help explain how and why this happens. Tumor cells disrupt the body’s circadian clocks, interfering with how they make and use sugar and fats for nourishment, researchers found.

Paolo Sassone-Corsi of the University of California, Irvine believes the findings go a long way to explaining why cancer kills even as modern medicine destroys the tumors. And he thinks doctors may eventually be able to find a way to overcome this.

Paolo Sassone-Corsi of the University of California, Irvine believes that tumor cells disrupt the body's circadian clocks, interfering with how they make and use sugar and fats for nourishment. Courtesy of Paolo Sassone-Corsi

“We have clocks everywhere, in every tissue in our body,” Sassone-Corsi said. “All these biological clocks need to be synchronized, or work in concert.”

“All the work that the liver has to do ... is now rewired to serve the tumor."

Sassone-Corsi studies how these internal clocks are re-set regularly by sunlight and by food.

But he was interested in whether cancer disrupts the delicate system, which governs some of the genes involved in metabolism.

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His team studied mice with lung tumors, examining their liver tissue almost hour by hour as the tumors grew.

They found that liver cells became more and more disrupted as the tumors thrived. The liver is the center for metabolizing sugar and fat. It stores vitamins and filters out toxins, so disrupting the liver can make an animal sick very quickly and, over time it’s fatal.

In the mice with lung tumors, many of the functions were off, the team reports in the journal Cell.

Related: Sugary Diet Raises Lung Cancer Risk

“All the work that the liver has to do in terms of glucose metabolism, lipid metabolism is now rewired to serve the tumor,” Sassone-Corsi told NBC News.

And it does this by hijacking the metabolic clock.

This might explain why cancer patients can often eat high-calorie foods, yet put on no weight, and it may help explain why sugary and high-glycemic diets appear to actually fuel tumors.

“We know how to somehow slow down or stop cancer. But don’t know how to take care of the rest of problem,” Sassone-Corsi said.

“We know how to somehow slow down or stop cancer. But don’t know how to take care of the rest of problem."

“Our study reveals that a lung tumor rewires liver metabolism along the circadian cycle,” he said.

They found that 46 percent of liver genes involved in circadian rhythm were changed by the tumors’ growth, some advanced by an hour in their patterns and some slowed by an hour or more.

This is almost certainly happening in other cells and tissues, Sassone-Corsi said.

He hopes it may be possible to alter diet and the delivery of cancer treatments to account for this shift, perhaps conquering the tumors’ effects on the body’s internal clocks.

Cancer cells put out all sorts of substances, from inflammatory compounds called cytokines to metabolic wastes. They can be measured, and they might be helping cause these changes as they circulate through the body.

The next step, Sassone-Corsi said, is to demonstrate the same phase shift in human cancer patients.