Symptoms can include rectal bleeding or anemia, abdominal pain or occult blood in the stool.
Such was the case with Guha, who was diagnosed in February 2011. He had settled in Phoenix with his wife and was getting a doctorate in environmental sustainability. The couple returned from a trip to India to visit his relatives and Guha developed abdominal pain.
"It seemed like the standard sort of bug issue when I get back from India," he said. "But it continued and got different, to the point where I was doubled up on the floor, and I was having trouble eating."
Because of his age, doctors never suspected cancer and looked at every other possibility, "including the plague," said Guha. A battery of tests were negative, but eventually a colonoscopy revealed a 6 cm.-wide tumor in the sigmoid colon.
When he saw a report that suggested it was malignant, Guha said, "I was in denial ? I thought surely there was another explanation."
MRIs and surgery revealed that the cancer had proliferated into his entire abdominal cavity -- a stage 4 diagnosis.
"It was pretty dire," he said. "But one of the things that makes it so deadly, is you have these metastases to distant organs like the liver, lung and brain and people usually die from organ failure."
But in Guha's case, the spread of cancer was confined to the abdominal cavity, a rare progression that doctors told him made the disease more treatable.
He had a colostomy, conventional chemotherapy, the removal of his gall bladder and a heated chemo bath of the lining of his stomach -- as the medical bills mounted.
By the time Guha had exhausted his insurance benefits, he had about $118,000 in medical bills. But now, future treatments will be covered under his student insurance plan.
"I take it day by day," said Guha, who was on a road trip to Idaho to serve as officiant at a friend's wedding. "It's quite likely that I'll have chemo again if [the cancer] pops up again. But I feel really good and I'm looking good."
So far, doctors say tests to determine if his early-onset cancer was genetic are all negative.
These cases of early-onset colon cancer that occur only in an individual and not in a family are a "rare event, not quite a black swan," said cancer expert Levine.
Guha is reassured that other family members may not suffer the same fate and also that his unusual case is hopeful.
"In the midst of what seems pretty scary, this is all working in my favor," he said. "I am younger and can handle the treatment better. The average age of a colon cancer patient is 71.4. My guess is most of those people are probably overweight and have comorbidities."
Just recently, doctors found one tiny spot of cancer on his liver, but a minimally invasive procedure called radio frequency ablation was able to kill it.
"It's not as if I think about the worst case scenarios all the time or I have the specter of death looming over me," he said.
"I could never get through life like that or be a productive member of society," said Guha. "I have always dedicated my life to doing something useful."
These days, he has dedicated himself to fundraising for more support for cancer patients and their families, especially Arizona's undocumented, who have no insurance.
Aetna spokesman Cynthia B. Michener said the insurance company would cover Guha's costs through the end of the plan year. His school's student plan just raised its annual limit to $1 million, and the new Affordable Health Care Act has eliminated lifetime limits, she said.
"While we are pleased to have found a solution for our member, we recognize that there is much more work to be done to fix the problems in our health care system," said Michener in a prepared statement. "We are committed to reforms that make the system work better for everyone."
Those who would like to learn more about Guha's charities can go to the University of Arizona Cancer Center's Patient Assistance Fund, the Colon Cancer Alliance or Wellness Community Arizona.