"I've asked people who are pretty involved in [the clinics] what the names of the doctors are or for medical records and 95 percent say 'no,'" said Barrett. "Once in a great while I've had someone offer records, but they were never traceable."
But Cousineau maintains that getting new cancer treatments approved is expensive and time-consuming for these clinics, which is why they choose to keep them under wraps — not because they don't work.
"I think the [clinics'] reputation is undeserved," said Cousineau, who is not a licensed physician. "The process to get a therapy of any kind approved in the U.S. takes a long time and is extremely costly. Just because they aren't approved doesn't mean they aren't working."
In addition to these alternative cancer clinics, patients may also seek what's known as "complimentary" treatments.
According to the American Cancer Society, everything from acupuncture to mediation to message therapy has been proven to help patients deal with anxiety and pain, both chief symptoms for cancer patients.
While accepting unproven and untested medicine may seem unwise to some, others who may feel like they've run out of options in the United States could see it as a last-ditch effort for a cure.
"I think it's human nature," said Len Lichentheld, deputy chief medical officer for the American Cancer Society. "Human nature is such that we always want to believe there is something else and so people become vulnerable to claims that somebody has something that is going to work."
"There are people who claim they've been helped, but you look at the data and you can't substantiate many of the claims, but still many will spend the money to send their relatives for a 'last try,'" said Lichentheld.
Patricia Chavez, whose mother visited one of the clinics in Mexico, told ABCNEWS.com that the treatment alone started at $9,000, but additional consultations and herbal medicines were added expenses. Doctors estimated that many alternative treatments cost in the tens of thousands of dollars.
"There are no viable 'alternatives' to mainstream cancer care," said Cassileth, who after 25 years as a cancer specialist said that she never saw someone cured by these methods. "There are dozens — probably hundreds — of spas and clinics that claim to treat advanced cancer successfully. None of them work."