Between 1990 and 2019 the global number of cancer cases in under 50-year-olds increased by 79 percent.
The number of deaths in under 50s also rose by 28 percent.
And the highest rates of early onset cancers in 2019 were in Australasia, North America and Western Europe.
The biggest killers were breast, trachea, lung, bowel and stomach cancers.
Dr Burton King is a breast cancer specialist in Te Whanganui a Tara Wellington, and he knows well the toll a cancer diagnosis can have.
"They are mothers, daughters, grandmothers, professional women, and absolutely remarkable people. Many women come here with anxiety about cancer."
While most of his patients are those aged 50 and over, Dr King says he's increasingly treating younger women.
"About 25 percent of our patients are under 50," he told Newshub.
"My youngest breast cancer patient is 22."
A new report in the British Medical Journal shows early onset cancers are on the rise.
Researchers found that while genetics may play a part, smoking, alcohol consumption and diets high in meat and salt were also factors.
"Lifestyle, especially exercise and weight management – those things are real concerns, and alcohol, for breast cancer is emerging as a risk factor," Dr King said.
But some experts also caution against reading too much into the findings - as the research did not take into account a 40 percent rise in the total population, or better reporting.
The study also couldn't make any firm conclusions on what's caused the increase in early-onset cancers.
But it did suggest better prevention and earlier detection measures.
"The benefits of early intervention and early diagnosis means that we can spend less on more advanced therapies, less on chemo, and less on hospital care," Dr King said.
"And action against cancer is going to need initiatives right across the cancer spectrum," said Cancer Society CEO Rachael Hart.
"So we want investment in prevention so more New Zealanders live cancer-free lives."
Because prevention could curb a worrying increase in young cancer patients and save more lives.
