Siddhartha Mukherjee’s life hasn’t been the same since his book on cancer was published in America. “This book thing has gone into total madness,” he laughs. “Actually, my publisher called and said, ‘You need to sit down and you need to open this email that I am sending you.’ It was incredible. I was literally speechless.”

His 571-page The Emperor of All Maladies: A Biography of Cancer, a humane account of an ancient disease that is expected to ravage India in the next 20 years, is the latest literary sensation in America.

Siddhartha cannot get over his publisher’s email concerning his book. “It has been called one of the ten best books of 2010 by The New York Times. I feel elated. The New York Times’s list of ten best books is the highest recognition in the book world.”

In its review, the paper called it a “powerful and ambitious first book… Mukherjee has undertaken one of the most extraordinary stories in medicine: a history of cancer, which will kill about 600,000 Americans by the end of this year, and more than seven million people around the planet.”

The author is in his New York laboratory — which has been called a “Stanley Kubrick-like space” — trying to get back to something approaching his routine existence. Still only 40, he is an assistant professor of medicine at Columbia University as well as a doctor dealing with cancer patients at Columbia University Medical Center.

Meanwhile, his book, published in November by Scribner, a division of Simon & Schuster, is flying off the shelves in America where for three weeks since publication it’s been on the bestseller lists. “My life has been turned a little upside down — the television media responds a little slowly but when it wakes up it goes completely bonkers,” he says on the telephone.

Not that Siddhartha is complaining. “It’s wonderful, an honour, a pleasure.”

His passion for his subject is so genuine it is hard not to share in his happiness. We had first discussed the book a year ago when it was being tipped as a “must read” for Oxbridge candidates, which had seemed odd because it had not even been published then. But word was filtering across the literary world that this biography of cancer, to be published in India by HarperCollins, was going to be “a big book”.

His literary agent is Andrew Wylie, feared and admired in equal measure across the publishing industry. His stable includes many top guns — from Salman Rushdie to V.S. Naipaul.

I tell Siddhartha that if nothing else, Wylie will make him a very rich man. Certainly, the book is living up to the early predictions. It has been sold in 12 languages already — any day now a pirated edition will appear on Indian pavements, the ultimate accolade for a bestseller. Among authors, Rushdie and Margaret Atwood have announced this is the book they are reading this winter.

Siddhartha, who has become something of a celebrity himself, has been on a TV show with Rushdie. His proud parents — his father retired from Mitsubishi and his mother was a teacher — have returned home to Delhi after witnessing the book’s launch. These days Siddhartha is continually on tour with only limited time for his wife, Sarah Sze, an artist, and their daughters, aged five and 11 months.

He admits to being consumed by his work and “intensely academic”, but comes across as naturally easy-going — which has been helping him win over audiences on his book tours.

“I’ve done several cities already,” he tries to recall. “What have I done? It’s such a blur. I did Houston, Boston twice, Toronto, Washington twice, couple of other places, where did I go? … Montreal. Boston, of course. In January I am doing San Francisco, Los Angeles, Seattle, Chicago, and Albuquerque (in New Mexico),” he says. “I have been asked to do the Jaipur Festival and I am certainly thinking of doing it on January 22.”

He knows the date when he will be in London — February 6. Extracts from his book will be serialised in a UK broadsheet. Then it will be the Netherlands and back to Britain, a place he knows well because he did his PhD as a Rhodes Scholar at Magdalen College, Oxford.

Siddhartha grew up in Delhi, graduating from St Columba’s School. It was at Columba’s that Siddhartha acquired a love of literature, especially Shakespeare, which perhaps explains why his answers are effortlessly fluent and well constructed. It could also have been the place which triggered his interest in cancer: his favourite English teacher died from it. At 18, he left Delhi, initially to do an undergraduate degree at Stanford. He returned to do research at Harvard Medical School after Oxford.

So what is Siddhartha? A Bengali boy made good, another triumph of an “American Indian” or yet another example of a potentially brilliant Indian whose genius has manifested itself because of the opportunities available in America?

“I feel very different tugs of identity and I enjoy that,” he admits. “One nice thing about America at its finest is that you don’t have to relinquish any piece of yourself to become part of America — that’s when America works at its best. I feel that about living here, particularly in New York where it is so global. There are days when I feel more Indian, there are days when I feel less so. Some of it has to do with the fact I practise medicine.”

He explains: “Medicine is in a fundamental sense a great equaliser. It breaks through barriers of identity in such crucial, poignant ways that by the very virtue of practising medicine you become a citizen of another place.”

He acknowledges President Barack Obama’s trip to India has had a huge impact on how the country is perceived. “There is no doubt that India has woken up in the public consciousness of America in a way that wasn’t even present 10 years ago. And I have lived here for so many years.”

There are other indicators. “There isn’t a day any more when there isn’t an article about India somewhere in The New York Times — often on its front pages. The articles themselves may point out things about India that one does not want but none the less the level of exposure is incredible.”

When Siddhartha comes to India —he visits his parents once a year — it will become apparent he possesses natural charm plus that rare gift of being able to untangle complicated scientific ideas, especially medical ideas to do with cancer, in language which ordinary people will be able to understand.

For example, what precisely is cancer? How does it spread? How do we prevent cancer? Indeed, can it be prevented? He is quite clear India is headed for trouble because tobacco companies, squeezed out of the West by powerful anti-smoking campaigns, are dumping cheap cigarettes in countries such as India. A cancer epidemic is inevitable unless the government acts.

Siddhartha is surprised I have read his book — “have you finished it, it’s a fat book”.

I ask him to unravel what he means when he declares he has a mission to “demystify” cancer.

“The book was written because even today for the vast public cancer remains a mystery, what the cause is, how it happens, what its origin is and how it gets treated,” he begins. “It is very important to emphasise that cancer is not a unitary entity, it is a family of diseases. There is an enormous level of diversity in cancer. I believe one only gets solace through understanding and so this book was an attempt to provide that kind of understanding.”

What about prevention?

“The answer is that we don’t know very much what not to do.”

In some ways, this is a strange answer because, as Siddhartha points out, “we know some of the culprits”. Tobacco, of course, plus asbestos, high doses of radiation, sunlight for those who have susceptibility to the sun’s rays (Indians suffer less from this), hepatitis B and C viruses and certain forms of bacteria are all “on a well established list”. But sometimes, medicines such as oestrogen replacement prescribed to relieve menopausal conditions can prove carcinogenic.

Back in his lab, Siddhartha outlines his current research. “We are trying to find cures for leukaemia based on our understanding of how leukaemias grow. That is when white blood cells become cancerous. I work on adult leukaemia.”

Siddhartha’s view is that cancer is part of the human condition, especially in an ageing population.

This isn’t an easy question to ask but fiddling around all day with toxins, radiation and the like, is he not scared that he himself might get cancer one day?

“Yes, absolutely,” he responds cheerfully. “When you write about medicine, you are in a complicated way writing about your own mortality. My fear is less about my own mortality but about the people I love.”

He sums up his philosophy: “If we seek immortality, then so, too, in a rather perverse sense, does the cancer cell.”