Governments around the world are leaving millions of cancer patients to suffer needlessly because of their failure to ensure adequate access to pain-relieving drugs, an international survey claims.

"Unrelieved cancer pain is a cause of major worldwide suffering, not because we don't have the tools necessary to relive pain, but because most patients don't have access to the essential pain-relieving medication," Prof. Nathan Cherny, the study's lead author, said in a statement. "This pandemic affects literally billions of people. Not only are the patients suffering often terrible unrelieved pain, but their family members are often permanently scarred by the memories of witnessing such suffering in their loved ones."

Data for the study, which was presented at the ESMO 2012 Congress of the European Society for Medical Oncology in Vienna, was gathered between December 2010 and July 2012, with 156 reports submitted by experts in 76 countries and 19 Indian states.

These reports represented 83% of 5.7 billion of the people living in Africa, Asia, the Middle East and Latin and Central America and the Caribbean.

The researchers say they found very few countries provided all seven of the opioid medications that are considered to be essential for the relief of cancer pain by the International Association for Hospice and Palliative Care.

It added that in many countries, fewer than three of the seven medications are available and those that are available are either unsubsidized or poorly subsidised by government, and availability is often limited.

Cherny says the study can be used to lobby governments to implement plans to treat cancer pain and to ease regulatory barriers so patients can access the necessary medicine.

"We are determined to tackle this problem at every level," Cherny said.

He said the presentation in Vienna was the beginning of "an organized and coordinated effort to take on one of the major global public health challenges of our time --the effective relieve of cancer pain for all cancer patients, wherever they may be."