Cases of cancer among people aged 14 to 49 rose by nearly 80 percent, from 1.82 million to 3.26 million, between 1990 to 2019, according to the study published in the journal BMJ Oncology.

While experts cautioned that some of that increase was explained by population growth, previous research has also indicated that cancer is becoming more commonly diagnosed among under-50s.

The international team of researchers behind the new study pointed to poor diet, smoking and alcohol as major risk factors underlying cancer in the age group.

But "the increasing trend of early-onset cancer burden is still unclear," they added.

A little over one million people under 50 died of cancer in 2019, up 28 percent from 1990, the study said.

The deadliest cancers were breast, windpipe, lung, bowel and stomach cancers, according to the study.

Breast cancer was the most commonly diagnosed over the three decades.

But the cancers that rose the fastest were of the nasopharynx, where the back of the nose meets the top of the throat, and prostate.

Liver cancer meanwhile fell by 2.9 percent a year.