LONDON (Reuters) - Many of the world’s top drugmakers are not doing enough to provide medicines to poor countries, leaving big gaps in access to treatments in crucial disease areas, including cancer, according to a new report on Tuesday.

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The non-profit Access to Medicine Foundation (AMF) found companies overall were doing more than in the past to reach under-served populations, for example by setting lower prices for some drugs and improving transparency surrounding patents.

But many such strategies address only a limited number of diseases and are often confined to just a few countries -- principally large emerging markets such as China, India and Brazil.

What is more, research into urgently needed medicines for the developing world now relies on just a handful of companies, creating a fragile ecosystem where cutbacks by one player could have a significant impact on future supplies.

In the case of cancer, specific access initiatives are in place for only 5 percent of experimental medicines by the time they reach the market, even though two-thirds of all cancer deaths now occur in low- and middle-income countries.

By contrast, access plans are established for more than half of drugs for infectious or communicable diseases at the time of launch, reflecting a major global drive to improve the rollout of treatments for conditions such as HIV and hepatitis.

“The gaps are still plenty,” said Jayasree Iyer, executive director of the Amsterdam-based foundation. “It’s critical that the pharmaceuticals industry makes sure its innovations are not leaving people in the developing world behind.”

The AMF’s ranking of the world’s top 20 drug companies by their commitment to access, published every two years, placed Britain’s GlaxoSmithKline top for a sixth time, despite recent cuts in its African operations.

Switzerland’s Novartis, U.S.-based Johnson & Johnson and Germany’s Merck KGaA made up the rest of the top four, followed by Japan’s Takeda Pharmaceutical, which was the biggest riser in the league table.

Significantly, 63 percent of R&D projects identified as high priority for people in poor countries are now being conducted by just five companies -- GSK, Novartis, J&J, Merck KGaA and Sanofi.

The four bottom-listed companies in the access rankings were U.S. groups Eli Lilly and AbbVie, and Astellas Pharma and Daiichi Sankyo of Japan.

The index, which is sponsored by the Bill & Melinda Gates Foundation and the British and Dutch governments, has built up a following among both drug company executives and investors, who are anxious to ensure companies meet societal commitments.

It is the first time that the survey has looked in detail at cancer -- currently the hottest area of pharmaceutical research and one that has produced some of the industry’s most expensive products.

“Some people believe that new, innovative products for cancer will never reach the developing world -- but we think it will happen and the companies planning for that will be able to offer the right medicines to the right people,” Iyer said.