(CNN) -- A cancerous tumor in 13-year-old Danny Hauser's chest has shrunk significantly since he was ordered by a court last month to resume chemotherapy treatment, a family spokesman said.



Danny Hauser, 13, was headed for a clinic in Mexico until an arrest warrant was issued for his mom.



But the Hauser family attributes much of his progress to the complementary use of vitamins and minerals to boost his immune system, Dan Zwakman said.



"The family is doing it on their own, with the doctor's knowledge," Zwakman said. "Everybody is pleased that the tumor is shrinking, of course. The goal is to get rid of the cancer, but they'd rather be doing it without the chemo."



Danny's case made national headlines last month when he and his mother, Colleen, fled Sleepy Eye, Minnesota, for Mexico to seek alternative cancer care despite a court order that he undergo chemotherapy.



They eventually returned after an arrest warrant was issued for Colleen Hauser. But had they made it to their destination -- the Rubio Clinic in Tijuana, according to Zwakman -- they would have joined the ranks of an estimated hundreds of other cancer patients who head south of the border each year for cancer care.



"Their intentions started long ago with Colleen. She's been involved in natural healing for many years now. She believes the world was created with everything needed to sustain and heal life," Zwakman said.



Despite controversial origins and consistent bad press in the United States, Tijuana's border clinics continue to attract people like the Hausers, who are in search of more holistic approaches to cancer treatment.



Because little data exist on how many clinics are operating, it's unclear how many American cancer patients visit Mexico each year, said Stephen Barrett, a patient advocate who runs the Web site, http://www.quackwatch.com/.



"If they answered, you could not be sure they were telling the truth. They might have an incentive to raise the number," he said in an e-mail. "To make matters more complicated, many of the 'cancer' clinics also see people who don't have cancer."



The concept of complementary and alternative cancer treatment has slowly been gaining acceptance for more than a decade in the United States, with the creation of entities including the National Cancer Institute's Office of Cancer Complementary and Alternative Medicine.



"Clinicians and researchers have realized that it's important to conduct methodologically sound studies to help guide patients to understand what's safe and what's effective," said Dr. Ted Gansler, medical director of health content for the American Cancer Society.



But no one recommends that alternative treatment be used to replace conventional care, such as chemotherapy or radiation, he said.



"The important thing to remember is there is no recommended alternative to conventional treatment, and the reason is because if it worked, it would become conventional," he said.



As far as Tijuana's border clinics are concerned, the American Cancer Society cautions that "methods promoted in Mexican border clinics are not consistent with scientific understanding" of cancer and its treatment.



"Although these clinics often claim great success in advertisements and books, they have not published convincing evidence in medical journals to support those claims," the ACS says in a section on its Web site called Questionable Cancer Practices In Mexico. "Patients traveling to the Tijuana area for treatment appear to be subjecting themselves to costly and potentially hazardous regimens, especially if they postpone standard medical care."



Loose regulatory standards in Mexico allow Tijuana's clinics to thrive, many offering expensive treatment in luxurious, spa-like settings, complete with fresh meals, exercise classes and emotional and spiritual counseling.



Many herbs and dietary supplements used in border clinics are not considered dangerous; they just have not been put through the rigorous clinical trials required for the U.S. Food and Drug Administration to approve them for use as cancer treatments.



Others, like the antioxidants carotene, lycopene and vitamins C, E and A, have produced inconsistent results in large-scale trials and are still being researched. Still others, like laetrile,
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