When Almut Schulze thinks of cancer, she thinks of genes and molecules. As she squints through the microscope at a slide of malignant cells, she muses why these cantankerous masses of protein multiply in an uncontrolled manner, and wonders whether she might one day find a way of stopping them. What doesn't enter her mind, she says, is a person, the person with the disease. As a molecular biologist working for Cancer Research UK, this might be expected, but for one thing. On January 31 this year, her husband, Ivan, died of a brain tumour.

Two and a half years ago, Ivan Noble's life couldn't have been better. He had just landed his dream job as a science journalist working for the BBC News website in London and had not long met his German girlfriend, Almut. The two had recently bought a house together and celebrated the birth of their first child, a girl. "We were on top of the world," says Schulze.

And then, in September 2002, after returning to the UK following a stint reporting in West Africa, the headaches started. The kind of headaches that won't be banished with an aspirin or some ibuprofen, the sort that wake you up in the night. Noble went to see a GP and was referred to hospital.

Though not a medic, Schulze initially thought Noble had picked up a tropical disease on his travels. And then they did a CT scan and a lung scan, and the alarm bells started ringing. From her scientific work, Schulze knew that a lung scan would tally with the doctors looking for brain metastasis of cancer, the spread of a malignant tumour from one part of the body to another. It didn't look good.

They did a biopsy and three days later the diagnosis came: Noble had a brain tumour. As the doctor put it: "There are no good tumours to have, but if there were, yours would not be one of them."

"When we got his diagnosis it was like losing the ground beneath our feet," recalls Schulze. "Things like 'Where are we going for holidays next year?' or 'When our daughter goes to school ...' just didn't mean anything any more."

The textbook name for his disease was Glioblastoma Multiforme. Schulze had heard of it, but knew little about it. "So I had to learn," she says, "just like any other relative of a cancer patient." What she found made grim reading. Cancers tend to be judged in terms of their five-year survival rate: five years after diagnosis, what percentage chance is there of the patient still being alive? For Noble, it was less than 5%.

While Schulze immersed herself privately in researching the tumour, filtering the information for her partner's consumption, Noble decided to write publicly about his disease. He wrote an online diary of his life and treatment which he kept until just before his death earlier this year. The blog, which featured on the BBC News website, had a huge following. Every time a new instalment was posted, Noble was deluged with emails from well-wishers, many of whom had experience of cancer and wished to offer him their support and, often, their survival tips. Through the course of his illness, he and Schulze married and, six months before his death, welcomed a son into the world. Three hundred thousand people logged on to read his final entry.

Before he died, Noble agreed that the diary should be made into a book, Like a Hole in the Head, with all profits to go to Médecins sans Frontières. Schulze is "very proud" of the book, although she admits to not being very keen on the diary when he was alive. "I found it distressing, obviously, but it was also an uncomfortable reality check. I rarely read it, but when I did, there was no denying that it was really happening. I also didn't like the idea of our personal lives together being exposed like that, but we discussed it, and I could see the benefit of it for him, so I agreed."

Schulze, naturally a shy person, made Noble promise not to mention her or the children by name in the diary and is only doing interviews because the book is for a good cause.

Because of her expertise, Schulze admits that her reaction to the diagnosis perhaps differed from those with no specialist knowledge. "Maybe I was a little more pragmatic about it. Maybe I had a little bit more hope, a bit more confidence in the treatment than other people might have. Also, I wasn't so scared by the word 'cancer' as such because it's something I deal with on a day-to-day basis. I know about survival rates and I know that it's not necessarily a death sentence."

After the diagnosis, Schulze wasn't sure if she could continue her work at Cancer Research. "I'm exposed to the subject every day and I came across papers regularly that mentioned his condition," she recalls. "They always began: 'Glioblastoma is a notoriously difficult tumour to treat, the survival rate is ... etc etc'. I was also angry. I was angry that even though we know so much about cancer, science couldn't offer Ivan more, that we couldn't offer him better treatments."

After a few weeks, Schulze decided that she would continue her work. "At the end of the day, it's my job and I can't do anything else."

Though she has a scientist's rationality, Schulze admits she always held out hope that her husband might defy the statistics. "I am not religious. I know there are no miracles," she says, "but I also know that biology is more complex than we think. It would be luck if he survived, not a miracle. Even though the five-year survival rate is less than 5%, it's still 5%. Ivan might have been one of the 5%. Even though it was quite unrealistic, I held on to this hope."

Like anyone caring for a loved one who is seriously ill, Schulze struggled most with the ordinary, little things. "Ivan stepped out of doing the everyday things," she says. "He did what he could, but as a cancer patient there's always something that needs doing - doctor's appointments and treatments, and Ivan had counselling and did t'ai chi."

"You're living somebody else's life. Everything rotated around Ivan and his wellbeing." It was difficult, she admits, getting her own life back. "The first week after he died, people said things like, 'Oh, it must have been a relief in the end', but I think that's completely wrong. There was a feeling of relief, but in relation to me, not Ivan. I felt like I had been ill too and when he died, I felt well again, and so was relieved in that sense. It wasn't a relief that it was over for him, even though he suffered a lot in the end."

Five months on, and Schulze is back at work. She is now considering redirecting her research to focus on the kind of tumour her husband had. If anything, the experience has reaffirmed her faith in science. "I sincerely hope the work I and others are doing will be able to help people like Ivan and make such suffering a thing of the past." And she adds: "I'm pretty sure that we'll be able to do it."

· Like a Hole in the Head by Ivan Noble is published by Hodder & Stoughton, priced £6.99. All proceeds go to Médecins sans Frontières.