In May 2010, he was diagnosed with a stage 4 brain tumor. Cashy, as he is affectionately called, spent 10 months at a Salt Lake City hospital enduring high-dose chemotherapy and a bone marrow transplant.
His tumor was inoperable, inextricably wrapped around his optic nerve.
Cashy's father, Mike Hyde, said he was so sick, he hadn't eaten in more than 40 days. He was so sick, he was vomiting eight to 10 times a day and couldn't lift his head off his pillow.
"They asked us six to seven times if we wanted to quit efforts and just let him go," said Cashy's mother, Kalli.
Cashy's parents made a radical decision. They asked Cashy's doctors to take him off his anti-nausea and pain medications.
Instead, Cashy's parents turned to cannabis oil, made from marijuana. It's a substance that is illegal under federal law.
Kalli Hyde, a registered nurse, and her husband began sneaking the cannabis oil into Cashy's feeding tube. They did not inform Cashy's oncologist.
Cashy's appetite returned. The couple says Cashy slept more and appeared to be in less pain, all of which seemed to help the boy endure the grueling chemotherapy.
"Within 2 weeks time, Cashy was off all those drugs. He was sitting up in bed eating, he was laughing," the father said. "The doctors and nurses told us that it was a miracle and amazing."
In January 2011, the parents say doctors told them Cashy was in remission, but the family's joy was short lived. An MRI in October 2011 showed Cashy's tumor had returned. That's when their second cancer fight started.
Marijuana is classified as a Schedule I drug by the Drug Enforcement Administration. That means the DEA believes marijuana has "no currently accepted medical use" and has a "high potential for abuse."
Trying to change that, the California Medical Association recently urged the federal government to make it easier for scientists to conduct more medical research on marijuana.
"I think there is tremendous potential for using cannabinoids for treating cancer," said Dr. Prakash Nagarkatti of the University of South Carolina School of Medicine.
"Cannabinoids" are the chemical compounds unique to marijuana, or cannabis.
Researchers like Dr. Nagarkatti see promise.
"We can use these cannabinoids to activate those receptors that are found on cancer cells and thereby be able to kill the cancer cells," he said.
Dr. Nagarkatti and his team of researchers were among the first to show that the active compounds in cannabinoids can target a cancer cell, unlock the receptor and direct the cancer cell to self-destruct.
"When you inject marijuana cannabinoids called THC into mice, we found that almost 25% to 30% of the mice would reject the cancer or reject the tumor," Nagarkatti said. "The cells basically commit suicide and they die."
Dr. Nagarkatti's results in mice are so promising, he's beginning human clinical trials with leukemia patients.
"Cashy's not a criminal," Mike Hyde said. "Cashy just wants to live. Cashy wants to go outside and play."
Cashy's second bout with brain cancer brought the family to Southern California's Loma Linda University Children's Hospital for six weeks of proton radiation.
Once again, the parents did not tell Cashy's doctors about the cannabis oil out of fear his treatment would be stopped. They did not get Cashy a medical marijuana recommendation for California.
"Prosecution is not my worry. Cashy turning 4 is my worry. If Cashy can turn 4 and I'm sitting in jail, that's fine," the father said.
The Hydes believe so strongly in the power of cannabis, they both say they use marijuana themselves.
The mother, six months pregnant, said she smoked marijuana for pregnancy-related nausea.
"I just want to spread the word to other parents," she said. "They need to know that he is flourishing on this medication."
Cashy's brain tumor shrunk by half during six weeks of radiation therapy at Loma Linda. But the potential for marijuana to act on cancerous tumors isn't known yet.
"Cannabis is felt to act in a number of different ways against tumors and one is by blocking angiogenesis or the creation of new blood vessels," said Dr. Donald Abrams, an oncologist at UC San Francisco.
Cashy's battle with cancer is far from over, but it's a fight his family won't back down from.
"Cashy has cancer and we're fighting cancer. Cancer has no rules, and neither do I," Mike Hyde said.
It's been about seven weeks since Cashy completed his radiation at Loma Linda. The tumor has continued to shrink.
Cashy's parents say the MRI scans they got last week show the tumor is gone for now. He is in remission again.
A foundation has been established in Cashy's name. The Cash Hyde Foundation buys wagons and customizes them with IV poles and stickers and donates them to hospitals.