I think the way we think about cancer, the way we treat cancer, has dramatically changed in the last century. There is an enormous amount of options that a physician can provide today, right down from curing patients, treating patients or providing patients with psychic solace or pain relief.
I left Delhi in 1989 and remember very little of how life used to be then. Increasingly, in my recent visits to Delhi, I've started to realize that the city has become intellectually very lively. It makes me want to discover the city over and over again.
I wanted to explore cancer not just biologically, but metaphorically. The idea that tuberculosis in the 19th century possessed the same kind of frightening and decaying quality was very interesting to me, and it seemed that one could explore the idea that every age defined its own illness.
Cancer has enormous diversity and behaves differently: it's highly mutable, the evolutionary principles are very complicated and often its capacity to be constantly mystifying comes as a big challenge.
A breast cancer might turn out to have a close resemblance to a gastric cancer. And this kind of reorganization of cancer in terms of its internal genetic anatomy has really changed the way we treat and approach cancer in general.
There is a duality in recognising what an incredible disease it is - in terms of its origin, that it emerges out of a normal cell. It's a reminder of what a wonderful thing a normal cell is. In a very cold, scientific sense, I think a cancer cell is a kind of biological marvel.
We don't know why, but pancreatic cancer has a very interesting physiological link to depression. There seems to be a deep link, and we don't know what it is.
I had seen cancer at a more cellular level as a researcher. The first time I entered the cancer ward, my first instinct was to withdraw from what was going on - the complexity, the death. It was a very bleak time.
There's a phrase in Shakespeare: he refers to it as the 'hidden imposthume', and this idea of a hidden swelling is seminal to cancer. But even in more contemporary writing it's called 'the big C'.
Cell culture is a little like gardening. You sit and you look at cells, and then you see something and say, 'You know, that doesn't look right'.
There's a rising cancer trend and, as I said, one of the major contributors is the overall ageing of the population - we aren't dying of other things, so we're dying of cancer.
Probably the most important reason we are seeing more cancers than before is because the population is ageing overall. And cancer is an age-related disease.
If there's a seminal discovery in oncology in the last 20 years, it's that idea that cancer genes are often mutated versions of normal genes.
I began wondering, can one really write a biography of an illness? But I found myself thinking of cancer as this character that has lived for 4,000 years, and I wanted to know what was its birth, what is its mind, its personality, its psyche?
What does it mean to be an oncologist? It means that you get to sit in at a moment of another person's life that is so hyper-acute, and not just because they're medically ill. It's also a moment of hope and expectation and concern.