Issued ahead of World Cancer Day on Wednesday, their report said more than 12 million new cases of cancer were diagnosed worldwide in 2008, resulting in 7.6 million deaths.
More than half of all new cases and around 60 percent of the fatalities occurred in developing countries, where poor medical infrastructure often means that cancer is a sure-fire death sentence.
"Cancer in the developing world is a hidden crisis that goes largely unreported, undiagnosed and untreated," said David Kerr, a professor of clinical pharmacology and cancer therapeutics at the University of Oxford, who contributed to the report.
"Cancer survival rates in developing countries are exceptionally poor. Lack of awareness, stigma and reliance on traditional healers mean most people do not seek medical help until their disease is advanced, and often incurable."
According to the report, issued by health foundation and consultancy Axios International, there could be 20 million new cases of cancer each year, and 13 million deaths, by 2030.
It points to several reasons why cancer -- which previously found a stronghold in rich economies -- is expanding so fast in poorer countries.
One is that people there are living longer, and the risk of cancer rises as one ages.
Another is the spread of modern lifestyles, characterised by smoking, drinking, little exercise and diets that are high in fat and sugar and poor in roughage.
But a third factor is cancers that are related to infection, such as the human papillomavirus (HPV), which is linked to cervical and colorectal tumours; liver cancer, linked to hepatitis B and C viruses; stomach cancer, caused by the bacterium Helicobacter pylori, and Kaposi's sarcoma, caused by the herpes virus.
Vulnerability has been boosted by immune systems that are damaged by the AIDS virus.
In low- and middle-income countries, the three most commonly diagnosed cancers are lung, stomach and liver in men, and breast, cervix and stomach among women.
But early warning infrastructure to alert people at risk-- and doctors and drugs to treat them effectively -- can be pitifully absent.
For instance, in the developed world, 63 percent of women have access to cervical screening, but this is only 19 percent in developing countries.
"Today, significant progress has been made in the early detection of many cancers, in particular breast and cervical, yet nearly four out of five people with cancer in developing countries are not diagnosed until they have late-stage disease," Axios' chief executive officer, Joseph Saba, said in a press release.
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