Many cancers have areas within them that are low in oxygen. In day two of our series on cancer research, health reporter Martin Johnston looks at four drug development projects at the Auckland Cancer Society Research Centre that exploit this feature to deliver a cancer-killing smart bomb that explodes only inside its target.

Ryu Kireka has been living with cancer for more than two years, but he isn't letting the disease hold him back.

The 7-year-old Auckland boy was diagnosed at age 4 with the T-cell type of acute lymphoblastic leukaemia (T-ALL), a rare and aggressive illness that is often less responsive to treatment.

His mother, Ana, simply thought he was having trouble shaking off a bad cold in August 2013, but when spots developed around his eyes she feared meningococcal disease and took him to Starship Children's Health where tests indicated cancer.

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Ana could hardly believe it at first.

"I thought they had come into the wrong room," she said.

Ryu was taken to the intensive care unit and started on treatment. He has been on chemotherapy since and is now receiving monthly maintenance doses plus daily pills, a regime expected to run until December.

Although Ryu has never been on a drug trial, Ana recognises the importance of developing new medicines for leukaemia.

X-rays at diagnosis revealed the mass on Ryu's chest which was making breathing difficult. Within 10 days of starting treatment, it was gone.

Ana says Ryu, the eldest of her three boys, has responded well to treatment and didn't lose his hair, to the surprise of everyone, including a cousin who had his own shaved off to support Ryu.

The worst effects have been a bout of anaphylaxis, which resulted in difficulty breathing and led to a change of chemotherapy, susceptibility to infections and leg weakness.

"He's really well. He's back to school. He plays rugby, he does rollerblading and swimming lessons. The swimming is helping with recovery of the weakening of his bones."

Researchers at the Auckland Cancer Society Research Centre are trying to set up a new trial of their drug PR-104 in young adults with T-ALL which is failing to respond to conventional therapy, although the trial is likely to be in the United States.

Ana welcomes the prospect of new medications being developed for Ryu's disease.

"I know a lot of other kids that have B-cell-ALL and some are on trials. I think we would have been willing to do it if he hadn't responded. They are never going to know [that a medicine works] unless they have people that are willing to do it."