He has undergone a human bone transplant in his tibia (shin bone) and has a titanium artificial knee.
Twelve rounds of intensive chemotherapy not only left him feeling terrible but prevented his body from making its own blood cells.
"They tried to blast it out of me," he said.
"It made me feel so horrible and sick I didn't want to talk to anyone. All I wanted to do was pull the curtains and curl up in a ball."
Liam needed several blood transfusions and in total received eight units of red blood cells and four units of platelets. The four units of platelets alone took 21 donors.
With Liam's enthusiasm to help others and with support from his school, he organised the blood service to visit Selwyn yesterday.
Sixty-six staff and students went to the school gym to give blood. A third were turned away as there are strict weight and height criteria.
Blood Service spokesman Paul Hayes said it was delighted it had 40 new donors.
Transfusions were an important part of most cancer patients' treatment, he said.
"Over 20 per cent of all red blood cells from donated blood are used for treatment of cancer patients. Many people think most donated blood is used for accident victims but this is not the case."
Tomorrow is World Blood Donor Day. "This is an opportunity to thank the New Zealanders who give up an hour of their time a few times a year to give blood," said Mr Hayes. "We are always looking for new donors, so it is good to raise the awareness."
New Zealand is one of very few countries that has enough people who voluntarily donate blood. It is able to produce enough blood and blood products to meet the needs of the population.
Osteosarcoma
* The most common type of bone cancer
* The sixth most common type of cancer in children
* Boys are more likely to get it than girls
* More likely to affect teens who are experiencing a growth spurt
* In most cases it affects the bones around knee (tibia and femur) or the upper arm bone closest to the shoulder (humerus)
Blood donations
* World Blood Donor Day - Friday www.nzblood.co.nz to donate blood (check eligibility and book an appointment)