Few parents would assume it was cancer when a sporting 16-year-old boy complains of swelling and pain in his calf.
Paddy O'Brien had finished playing in an all-schools water polo championships in Sydney when he had a crippling cramp in his right calf like a huge knot.
He attributed the pain and swelling to growing pains - maybe even a pulled ligament - similar to one of the many injuries he had acquired playing rugby, cricket, swimming and hockey.
When his usual physiotherapist massaged his leg, it caused such excruciating pain that Paddy was referred for an X-ray which, in turn, raised enough alarm that he was referred for an MRI.
But he had to wait two months because of the lack of services in rural areas.
It was May 2013, and Paddy was in Year 11 in Tamworth. Great things were expected of him in the HSC, so he tried to concentrate on his studies, but the pain was constant.
"I was in agony, I couldn't sleep, it was debilitating, I couldn't run, I couldn't walk. I told mum that my leg was in pain," he said.
His mother called the doctor, asking for an urgent appoint to request an MRI as soon as possible.
As they arrived, she said, "This better be bloody serious".
"I was in maths, fifth period, and the principal walked into class, and said he needed to see Paddy," recalled Mr O'Brien of the next day when he was told he either had Ewing sarcoma or osteosarcoma (cancer of the bone).
A few days later, he was diagnosed with Ewing, and the lump in the head of the fibula of his right leg was a malignant tumour.
It is very rare: only about 50 children on average each year are diagnosed with Ewing sarcoma in Australia, less than half of these diagnoses are in the 15 to 19 age group.
It is the same cancer that teenager Hannah Rye died from in August. Hannah's school formal was moved forward so she could attend with date Trent Hodkinson, a Newcastle Knights NRL player.
Mr O'Brien was among the first patients in Australia to be treated using the approach that is now being trialled in "Ewing 2008" around the world, including Australia and New Zealand. It increased the amount of chemotherapy by 50 per cent, lifting the amount to 14 intensive cycles of three days each. Half of the chemotherapy occurred before surgery to remove his fibula and a nerve - and the balance of chemotherapy after.
Despite "massive chemo brain" - difficulty forming sentences resulting in "massive grammatical errors", vomiting, lethargy - Mr O'Brien decided to continue at school, determined to finish the HSC with the friends who he had started school with 12 years earlier.
He had phantom pain and remembers that the chemo "massively screws up your bowels, your taste buds, your senses". His fitness went out the window.
A "very small silver lining" was that some of the pressure of the HSC was reduced. Although he ended up missing 60 per cent of the next year of school, he did well in his HSC and is now 21, and studying at Macquarie University.
He lost his hair each cycle, only for it grow back in fluffy tufts, and then to disappear again during the next round of chemotherapy.
"It is quite cool and weird from that sense," he said. "I lost all my hair - in my ears, eyebrows, underarms, eyelashes, everywhere. You wouldn't think eyelashes are that important but they definitely are."
Another silver lining, he added, was that he saved on shampoo.
"You have to have a humorous outlook on the whole situation, especially in hindsight. If you look back at it with resentment and a dark patch in your life that held you back you will never progress or move on.
"It is quite horrible, terrifying of course, but it dramatically shapes and changes you for the better. You discover new limits for your human body, specifically the interdependence of the body and mind. You also really get to discover who cares and who doesn't," he said.
While the survival rate for younger children with this cancer is about 70 per cent over five years, the rate is 60 per cent for young adults such as Mr O'Brien, said Vivek Bhadri, a medical oncologist at Lifehouse Cancer Hospital in Sydney, who treated him.
Nobody knows why the survival rate differs. And Dr Bhadri said the rate had not budged much since the 1980s, and experts hope the Ewing trial will improve outcomes for young people such as Mr O'Brien, who is cancer-free despite a few scares.
About a third of Ewing's sarcoma occurs in the leg, and in other long bones like the arms, that are rapidly growing in teenagers, said Dr Bhadri.
"That's when things can go wrong, and cancer can occur," he said.
Dr Bhadri said another reason why these cancers are not diagnosed faster is that injuries and growing pains are so common in teenagers that very few parents or experts would think the pain and swelling was caused by a cancer.