Washington: Pulitzer Prize winner, Siddhartha Mukherjee says there is no conclusive study linking the use of cell phones to brain cancer.

Indian American cancer specialist won the coveted honour for his first book 'The Emperor of All Maladies: A Biography of Cancer'.

But no study conclusively ruled it out, either, says Mukherjee, an assistant professor of medicine at Columbia University.

“Finding a causal agent for cancer is not like solving a mathematical equation. It's not like there is a single magical formula that will allow us to find and define a cancer-causing agent or carcinogen,” he told US National Public Radio (NPR) on Tuesday.

Mukherjee said the dramatic increase in usage of cell phones over the past two decades has almost (created) a natural experiment. “Because if the cell phones truly contain a carcinogen, then increasing cell phone use dramatically, as has happened, should increase the rate of development of brain cancers in America,” he added.

But that 'natural experiment' has not provided any evidence of a link, he says. Two major studies, he explains, show the rate of brain cancers between 1992 and the mid-2000s have 'essentially remained flat'.

A subsequent study found a small increase in tumours in women and not in men, but the increase was small - from 2.5 cases per 100,000 people to 2.6 cases per 100,000 - and occurred in the brain's frontal lobe.

Given the small numbers of cases and the very large numbers of participants involved in the study, Mukherjee said the incidence is likely to be a random fluctuation.

"You're vastly more likely, I suspect, to die of an accident because of the misuse of the cellphone while driving' than to develop a brain tumour," he said.

He hopes that two major trials under way in the US and Europe eventually "will settle the issue once and for all. But thus far, I would say the evidence remains pretty negative".