Firstly Stanislaw Burzynski (who I presume to be the "one person" you mention) isn't the only person to investigate antineoplastons, Ogata et al did a trial published in 2015, although that work is not without problems, it was completely unblinded for a start. Hardly top drawer science.
Secondly what Burzynski does isn't really clinical trials, he simply calls them that so he can keep charging victims through the nose for his scam, quoth Burzynski's lawyer Richard Jaffe they are:
artifice, a vehicle we and the FDA created to legally give the patients Burzynski’s treatment
As you'd expect, given that he's literally running these "trials" as an excuse to treat people Burzynski doesn't really publish his results, he published some shonky partial results once which only really served to underline the fact that antineoplastons don't work, they don't cancer - the only thing they can reduce the size of is the bank balance of desperate people and families.
The biochemistry of how Burzynski claims antineoplastons work just doesn't hold up:
Tracing the biochemistry involved in Burzynski's synthesis of antineoplastons shows that the substances are without value for cancer treatment.
By 1985, Burzynski said he was using eight antineoplastons to treat cancer patients. The first five, which were fractions from human urine, he called A-1 through A-5. From A-2 he made A-10, which was insoluble 3-N-phenylacetylamino piperidine 2,6-dione. He said A-10 was the anticancer peptide common to all his urine fractions. He then treated A-10 with alkali, which yielded a soluble product he named AS-2.5. Further treatment of AS-2.5 with alkali yielded a product he called AS-2.1. Burzynski is currently treating patients with what he calls "AS-2.1" and "A-10."
In reality, AS-2.1 is phenylacetic acid (PA), a potentially toxic substance produced during normal metabolism. PA is detoxified in the liver to phenylacetyl glutamine (PAG), which is excreted in the urine. When urine is heated after adding acid, the PAG loses water and becomes 3-N-phenylacetylamino piperidine 2,6-dione (PAPD), which is insoluble. Normally there is no PAPD in human urine.
What Burzynski calls "A-10" is really PAPD treated with alkali to make it soluble. But doing this does not create a soluble form of A-10. It simply reinserts water into the molecule and regenerates the PAG (Burzynski's AS-2.5). Further treatment of this with alkali breaks it down into a mixture of PA and PAG. Thus Burzynski's "AS-2.1" is nothing but a mixture of the naturally occurring substances PA and PAG.
Burzyski claims that A-10 acts by fitting into indentations in DNA. But PAG is too big a molecule to do this, and Burzynski himself has reported that PAG is ineffective against cancer [5,6].
PA may not be safe. In 1919, it was shown that PA can be toxic when ingested by normal individuals. It can also reach toxic levels in patients with phenylketonuria (PKU); and in a pregnant woman, it can cause the child in utero to suffer brain damage.
Burzynski has never demonstrated that A-2.1 (PA) or "soluble A-10" (PA and PAG) are effective against cancer or that tumor cells from patients treated with these antineoplastons have been "normalized." Tests of antineoplastons at the National Cancer Institute have never been positive. The drug company Sigma-Tau Pharmaceuticals could not duplicate Burzynski's claims for AS-2.1 and A-10. The Japanese National Cancer Institute has reported that antineoplastons did not work in their studies. No Burzynski coauthors have endorsed his use of antineoplastons in cancer patients.
These facts indicate to me that Burzynski's claims that his "antineoplastons" are effective against cancer are not credible.
So no-one is looking at antineoplastons because, people have looked and based on the evidence thus far they don't work, can't work and are just yet another predatory scam.