For Sam Mathias, it was a sore shoulder and strange sensations in his lungs that the fit 22-year-old dismissed as "little niggles".

At the time, he was finishing university, training in boxing and preparing to start a full-time banking career.

For chiropractor and occupational health researcher Angela de Weger, it felt like warm water running down her leg.

Neither imagined they were living with one of Australia's deadliest cancers.

"To be honest with you, I didn't," Mr Mathias says when asked if cancer ever crossed his mind.

"I think it was maybe just being a young fit man otherwise.

"I think I'm perennially a bit of an optimist as well."

For Ms de Weger, the explanation seemed just as reasonable.

"I didn't want to believe that it was anything more than that," she said after doctors suggested stress could explain her symptoms while she juggled full-time work, a research degree and raising her five-year-old son.

Months later, both would receive the same life-changing diagnosis: sarcoma.

The rare group of cancers can develop in bone, cartilage or soft tissue almost anywhere in the body, making it one of Australia's most difficult cancers to detect.

One in three Australians diagnosed with sarcoma will not survive beyond five years, yet the disease receives less than one per cent of Australia's cancer research funding.

It accounts for about one in five cancers diagnosed in adolescents and young adults.

Medical oncologist Dr Vivek Bhadri says there is rarely a single symptom that immediately points to sarcoma.

"There's no one specific symptom," he tells AAP.

"Oftentimes people will have non-specific symptoms."

Young people with persistent knee pain are often assumed to have sporting injuries or growing pains, while painless lumps elsewhere in the body could easily be dismissed, he explains.

"It's only when things haven't gotten better after several weeks that someone might go, 'Actually, you know, something's not quite right here. We need to do something else.'"

That was exactly what happened for Mr Mathias.

After about a year of brushing aside his symptoms, he noticed a lymph node in his neck had enlarged.

Even then, the first biopsy never happened because the clinic that was supposed to perform the fine needle procedure sent him away for presenting as too young and healthy.

Only after severe chest pain prompted an urgent X-ray was he ushered straight to hospital.

Because his cancer presented so unusually, specialists spent another 10 to 12 weeks analysing tissue samples before sending them to an expert in Boston to confirm the diagnosis.

By then, the cancer had spread to his lungs, neck lymph nodes and bones.

One person, though, had recognised something wasn't right long before he did.

"God bless my mum," Mr Mathias says.

"She took these things a lot more seriously and encouraged me to get them checked out because otherwise, yeah, I don't think I would have."

For Ms de Weger, the diagnosis came after two years of intermittent symptoms culminated in what she thought was a stroke while sitting at work.

Scans revealed a brain tumour.

A nine-hour operation later, doctors discovered it was a rare grade-three brain sarcoma.

Despite spending more than 35 years working in health, she was blindsided.

"I thought, 'I'm healthy, I live a good healthy life and didn't think it could happen to me'," Ms de Weger tells AAP, her thoughts immediately turning to someone else.

"I thought, 'well, what does this mean for my son?'

"Straight away I went into ... doing my will, doing all of those things, going into that mode, you know, trying to protect the future for him."

Dr Bhadri says these are stories that highlight why awareness remains critical.

"The earlier we make the diagnosis, the sooner we can start treatment and the better the outcome," he says.

He urges anyone with a lump larger than a golf ball, particularly one sitting deep beneath the skin, to seek medical advice. Pain that fails to improve or wakes people at night should also be investigated.

Eight years after her diagnosis, Ms de Weger considers herself "one of the lucky ones".

Although she continues to live with balance issues, cognitive fatigue and permanent hair loss from radiation treatment, she now sees advocacy as part of her recovery.

"I feel obliged to advocate," she says.

"I feel like my duty now to speak for people that can't speak for themselves or their families."

Her advice is simple.

"Listen to that little voice when you think, you know, something's not quite right," she says.

"And it's OK to ask for second opinions and it's OK to ask for that scan."

Mr Mathias, now 29, has undergone multiple rounds of chemotherapy, lung surgery, brain surgery and an experimental CAR-T cell therapy trial after conventional treatment options were exhausted.

Living with a rare cancer has changed how he measures life.

"It's the type of thing that makes you realise, and it's a cliche, that ... every day is a gift," he says.

The Australian and New Zealand Sarcoma Association hopes to raise funds through its Great Sarcoma Plank-A-Thon during Sarcoma Awareness Month to fund research and clinical trials.

The organisation says previous efforts have supported research leading to PBS access for the immunotherapy drug pembrolizumab, Medicare-funded whole-body MRI screening for people with a high-risk gene variant and a clinical trial identifying treatment for a rare sarcoma in teenagers and young adults.

For Mr Mathias, however, success starts with one simple outcome.

"I think the first pillar is awareness for young people and getting the word out there in terms of taking symptoms seriously," he says.

"If we can just get one person to receive an earlier diagnosis and a better prognosis, that would be a big win."