Liz Szabo

USA TODAY

The Food and Drug Administration has given a controversial Houston doctor the green light to resume administering experimental cancer treatments.

The FDA has lifted restrictions on a clinical trial run by Stanislaw Burzynski, who was the subject of a USA TODAY investigation last year. Burzynski, 70, has wrangled with state and federal medical authorities for nearly 40 years over his claims that he has discovered natural substances that can fight certain cancers.

Burzynski — hailed as a maverick by his fans but derided as a snake oil salesman by mainstream doctors — has long claimed to have achieved dramatic success in hard-to-treat cancers, especially brainstem tumors that are usually considered fatal. According to the National Cancer Institute, however, Burzynski has not produced proof that his drugs save lives by publishing a randomized, controlled trial in a peer-reviewed journal.

The FDA placed Burzynski's clinical trial on a partial hold — barring him from enrolling new patients — after the 2012 death of a 6-year-old New Jersey boy in his study.

Last year, the FDA issued a sternly worded warning letter to Burzynski, expressing concern about patient safety and the accuracy of his records.

In a statement issued Wednesday), the FDA confirmed that it has lifted its restrictions on Burzynski because he answered all of their questions. In particular, Burzynski addressed "common and serious (and in some cases fatal) adverse drug reactions, as well as accurate information on how often tumors shrink after treatment with antineoplastons."

In a statement, the Burzynski Research Institute says it is planning to launch a large, definitive trial — called a Phase 3 study — of patients with newly diagnosed brainstem tumors.

The FDA's decision "marks an important step in the development of antineoplastons for the treatment of various forms of brain tumors," the institute said in its statement.

Some cancer specialists say they're disappointed by the FDA's decision and concerned for the safety of young patients. Critics also say they're concerned about the financial impact on dying patients or their families, who often organize elaborate fundraising efforts to obtain the $100,000 or more needed to pay for Burzynski's experimental treatments, which are not covered by insurance.

"This puts patients at risk," says Peter Adamson, chairman of the Children's Oncology Group and chief of clinical pharmacology and therapeutics at the Children's Hospital of Philadelphia. Research has shown that antineoplastons can cause serious and even life-threatening side effects. "Exposing patients to ineffective therapies does not offer a meaningful prospect for benefit and only exposes patients to risk."

Given the FDA's past dealings with Burzynski, Adamson says its decision is "indeed sad, but perhaps not surprising."