In November 2012, he started a plant-based diet, alkaline diet - akin to that of Tom Brady - with his vegetarian wife Amanda, now 39, following research that showed sugars and processed foods fuelled tumours.
When it came to his next scan in early 2013, the cancer had shrunk by almost 80 per cent.
Now he is celebrating five years cancer-free, raising 20-month-old twins, and running a small cancer charity on the side of his bartending to help other sufferers afford pipe dreams - and his story has gone viral, after it was tweeted by country star Tim McGraw.
Speaking to Daily Mail Online, Rob admitted he was slightly overwhelmed at being tipped as a vegan advocate. "I'm not standing on my soap box saying everyone needs to go plant-based and vegan," he insisted. "But if you're going to ask me what worked for me, I'll tell you: this diet."
When Rob was diagnosed he was shocked, having no family history of cancer and already living a healthy lifestyle of running regularly and eating a lean protein diet.
"I couldn't believe it," he told Daily Mail Online. "I was always a healthy person, I didn't expect it."
He had been experiencing some symptoms for about a year, such as bloating and blood in his stool and a change in bowel movements, but he assumed it was IBS or something he had eaten, and without health insurance, he had decided to put it off.
It was not until July 2012 that he was hospitalised with searing pain in his abdomen. It turned out to be a micro-perforation of his colon, which meant nothing could pass by his colon. Doctors discovered cancer throughout his body, which had likely been lingering for two years.
"It was very very painful," he said. "I went into the ER and that's when I became an in-patient: they found it spread all around."
Determined to fight the disease, Rob began the gruelling regime of operations and chemotherapy and radiation therapy.
"It was horrible," he said. "I had to take time off work, I had no energy, I felt sick. That kind of medicine puts so many chemicals in your body."
At the time, Rob, who had moved to Las Vegas from Los Angeles a year before, was in the early stages of a new relationship with his now-wife Amanda, a cocktail waitress who worked at the same bar as his, the Cosmopolitan. They had been together for about nine months.
"She came into the hospital, the doctor took her to one side and said basically that there was about eight percent chance I would live," Rob explained.
"She was so upset, my family was so upset. The doctors weren't really telling me all of this but I knew it was serious, I thought I was going to die.
"But Amanda just stuck with me. She could have left me, but she stayed. That's when you know love is true."
The couple got engaged there and then ("I think I had a catheter in... it really wasn't very romantic but we didn't have time for the whole 'down on one knee thing', I was weak").
Then, two days after his operations, they got married, just before he embarked on chemo and radiation therapy.
From the moment of his diagnosis, he was eating as clean as he could because "I just wanted to be as healthy as possible", which was made easy by the fact that Amanda has always been a vegetarian.
After finishing his first load of treatments in November 2012, he decided to take it a step further and go vegan.
"At first I wasn't all raw and vegan, it was just vegetarian," he told Daily Mail Online.
"To be honest, it was easier for us to just cook one meal rather than two, so being plant-based was straight-forward.
"But when I finished chemo, the oncologists were saying I would need to do more straight away and I really didn't want to. I needed to heal. That's when I knew I needed to do anything to beat this cancer. I was really willing to try anything to save my life. That's when I went hard-core raw, vegan, superfoods."
It started with Rob looking up some alternative therapies he could try, including a treatment center in Tijuana, Mexico, which has been popular among American colon cancer patients.
However, it costs thousands of dollars in travel and medical fees.
Instead, he researched their detox to see if he could try it at home. It consisted of cutting out all acidity and sugars from his diet, including red meat and dairy.
"I went back in for my CT scan in early 2013, and everything had changed," Rob explains.
His cancer had shrunk by 80 per cent. Asked if he wanted to continue with treatments, he declined. By 2014, there was no trace of the cancer.
Now, Rob and Amanda are new parents to one-year-old twins, a boy and a girl, having undergone IVF ('because the treatment affects your swimmers a bit').
He said he hopes other patients do not take this as a blanket endorsement for veganism but rather urges people to educate themselves about all their options, and to consider the healthiness of their lifestyle.
Rob's story comes amid a surge in the rate of young people being diagnosed with colorectal cancers in the United States, while rates drop in the Mediterranean. Some reports have suggested this could be down to the Western diet, which is rich in processed meats, sugars and saturated fats.
