Aaron, now 20, contracted a type of blood cancer called lymphoma, in his intestines. Bed-bound for eight months, when he was finally discharged from hospital he did not remember how to walk.
But Aaron was determined to bounce back and live life to the fullest.
Now young men, he and fellow childhood cancer survivor Sam Ho King-sum recently took part in a sports camp that is intensive and challenging enough to put off the healthiest participants. They sailed, hiked and rode as well as the fittest athletes would.
Aaron could not make sense of the pain, the ban on eating, and the isolation from classmates when he was confined to bed for long periods of time.
It was a depressing and stressful time for him and his family.
"Months into the therapy, I once asked a doctor on duty whether I could eat yet," Aaron recalls. "But he refused and I threw a pillow at him in fury."
Aaron had a bumpy road to recovery. When he first returned to school, his appetite was poor and he had to wear a colostomy bag on his stomach to collect his bodily waste while his wounds healed.
Now 18, Sam learned he had a rare form of cancer called leiomyosarcoma, which affects the connective tissues of the body. He lost some of the muscles on his back during the surgery to remove the cancerous mass. His treatment left him bald for a while and he could not lift his left arm for six months.
As a triathlete and avid gym-goer, Sam was worried that the disease would spell the end of his athletic life. So he ignored his doctor's advice limiting his exercise and forged ahead with his regular gym visits. Following his instincts served to help: he has now fully recovered.
Physical wounds heal with time, but the mental scars often stay. Constant Wong Siu-wai, a counsellor from the Child Cancer Foundation, says parents often cannot let go of the notion that their children are vulnerable.
"This mentality often gives children the impression they are incompetent, sickly and require special attention," she says. "This can make them anti-social and over-reliant, preventing them from integrating into society."
This is why Aaron and Sam's participation in the sports camp is so important. They are determined to prove they need no special care. Along with seven other child cancer survivors, they braved Hong Kong's recent cold snap to join a four-day expedition organised by Outward Bound and designed for the physically fit.
"I do not want the experience of cancer to overshadow my life," Sam says. "I am capable of moving on, and ready for challenges."
In the first two days, they sailed a 20-metre yacht around Hong Kong and back to Sai Kung, the starting point.
They braved rough waters and sea sickness while learning how to manoeuvre a vessel, change sails and anchor the boat.
In the second half of the camp, they had to run and cycle around steep trails in the Sai Kung countryside during two, six-hour tasks.
"It was an unimaginably tough expedition," Aaron says.
"But if we could make it through cancer, nothing is impossible. A strong will and a positive attitude make the difference. People say the sun always returns after the rain."