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When Trevor Johnson was diagnosed with leukemia at the age of 4, he was treated with several rounds of powerful chemotherapy drugs and repeated blasts of radiation.

The cancer returned when he was 9, and the dose and duration of the treatments was raised to the limits of what his body could tolerate.

Today, at 23, Mr. Johnson is thriving, beginning a professional life in the sales office of the Toronto Blue Jays and enjoying life's little pleasures in a way that only a long-term cancer survivor can.

But the long-ago treatments have left their mark: The repeated spinal injections he underwent as a child have resulted in chronic back problems; the chemotherapy drugs damaged his heart, and the massive exposure to radiation stunted his growth and left him at high risk of developing more cancers in adulthood.

"I try not to think about that stuff and just enjoy life," Mr. Johnson said in an interview.

But with survival rates improving markedly and the vast majority of childhood cancer sufferers now living well into adulthood, researchers and clinicians are realizing that curing cancer can also have devastating effects.

Each year in Canada, about 850 children under the age of 14 develop cancer and 135 die of the disease, according to statistics released yesterday by the Canadian Cancer Society. (Cancer is the second most common cause of death in children after unintentional injuries, which claim 390 lives a year.)

Heather Logan, director of cancer control at the cancer society, said that two-thirds of children who survive a bout with cancer have at least one "late effect" - side effects that arise months or years after treatment - and one-third of those are grave or life-threatening.

"More children surviving cancer is welcome news, but more survivors are experiencing future health issues," she said.

The most common late effect among childhood cancer survivors is complications in hormone levels and metabolic changes that result in delayed puberty and infertility. Some suffer developmental problems that affect their education, and drugs can cause damage to internal organs such as the heart, lungs and stomach. The risk of more cancer is also quite high among survivors.

The good news, though, is that treatments have changed a lot and for the better, said Paul Grundy, director of pediatric oncology at Stollery Children's Hospital in Edmonton. Chemotherapy drugs are more targeted and less noxious, radiation is used in lower doses if at all, and there are alternative treatments such as surgery, lasers and freezing tumours to treat some cancers.

He noted that 82 per cent of those with childhood cancer now survive at least five years after diagnosis, and many for much longer. (Among adults, the five-year survival rate is a more modest 62 per cent.)

"As treatments change, so too will the late effects," Dr. Grundy said. One of the most dramatic illustrations of how cancer treatment has improved can be found in the story of Terry Hoddinott, owner of a company called Braille Masters in London, Ont.

Diagnosed in the 1960s with retinoblastoma, a rare form of eye cancer that is inherited, he underwent intense radiation treatment before losing both eyes at the age of 3.When Mr. Hoddinott's son, Riley, was born in 1996, he was diagnosed with retinoblastoma at one day old, and his treatment began within a week. Riley underwent chemotherapy, laser treatment and cryogenic probes to freeze the tumours, but no radiation. The boy lost one eye.

Advances in knowledge allowed for Mr. Hoddinott's daughter, Katie, born in 1999, to be diagnosed in utero and her treatment began 12 hours after she was born. She was treated with cryogenic probes and lasers (no chemotherapy or radiation) and appears to have been cured. Today, at age 9, Katie has 20/20 vision in both eyes.

"Our family is a prime example of how early detection and treatment can determine the success of treatment and the effects," Mr. Hoddinott said, adding that it is also a concrete example of the benefits of investing in medical research.

In 2008, an estimated 166,400 Canadians will be diagnosed with cancer and about 73,800 will die. About 40 per cent of women and 45 per cent of men will develop cancer during their lifetimes, and about one in four Canadians can expect to die of cancer.