Swimming in a Sea of Death: A Son's MemoirBy David RieffGranta Books £12.99 192 pagesFT bookshop price: £10.39

Susan Sontag died of leukaemia at the age of 71. It was her third experience of cancer: in 1975, at 42, she had been treated for stage IV breast cancer, which she had not been expected to survive. In 2004 she had had surgery and chemotherapy for uterine sarcoma. Her son's book is about her death. It is about her, inevitably, and it is also about the tensions that exist between cancer patients and their doctors, about changing attitudes towards cancer. Above all, it examines the stress and guilt of a person who has to watch someone they love die, slowly and painfully.

Oddly, Sontag's age at her final diagnosis is rarely mentioned. Most people who have tipped 70 are somewhat aware of mortality. Sontag was aware and violently resistant. She wanted to live to be 100 (more life to be experienced, more work under the belt), ignoring perhaps the truth that for most who live that long, both the quality of the experience and the appetite for work tend to plummet. She raged against the cancers - all three - and her attitude was one of what her son calls "positive denial": she refused to knuckle under, even to the final most damning diagnosis. Instead she went into overdrive, on a search for different doctors to consult and more radical treatments. In the case of the 1975 breast cancer, she had found a French oncologist who was then proposing an experimental form of chemotherapy ("another magic bullet ... that did not live up to its early promise"), the effects of which bordered on the unendurable. She survived, against all the predictions; perhaps she was just fortunate to buck the statistics, or perhaps as she would have believed herself, profiting from her own positive attitude.

This sounds unscientific, but David Rieff makes it clear that his mother had both faith and intense interest in science. She researched her own case ferociously on the internet; she interrogated her doctors. And she had herself attacked the imagery of cancer as a battle, a struggle - a kind of militarisation - in her essay Illness as Metaphor. She understood what cancer is and what it does, better than most patients. She must have been a challenging patient, and while you admire her spirit, her self-esteem can jar: her work is referred to "the work".

David Rieff is himself a writer of stature, and he is clear-eyed about his mother, though evidently devoted. He is angry with much of the current approach to cancer by those on the other side of the fence, those who don't have it but deal with it professionally. He is scathing about the ham-handed doctor who gave Sontag her diagnosis of myelodysplastic syndrome - MDS - which would "convert" into acute myeloid leukaemia - AML - with no preparation or apparent sympathy.

He is contemptuous of the language of those booklets which set out to advise and cheer cancer patients, written in the language of hope but effectively offering none to those reading with care, infantalising their readership.

One has to be careful here though, as there is cancer and cancer. Rieff is concerned with a particularly dire form; many are now successfully treated, many booklets are right to be encouraging.

Back in 1975, the standard practice for doctors was to lie to cancer patients. They do not today. They tend to offer a statistic. If dealt a "good" one, you can live with it, more or less. Otherwise - well, that is what this book is about.

For those of us who have ourselves experienced a cancer diagnosis, and who have also had the person they love die of cancer, to read this book is to step into a grimly familiar world. For others, it will be harrowing, revealing and will provoke thought.

David Rieff cannot decide if the knowledge available today is empowering or in fact an albatross - all that scouring of the internet. He is unsure if he said and did the right things when his mother was dying. Was he right to go along with her denial, to collude in her insistence that there could be a way out, her pursuit of ever-more radical treatment? Above all, he feels guilt - the awful irrational guilt of the survivor; "the living always fail the dying" - by being unable to stave off extinction. And he lashes out at Annie Leibowitz, his mother's "on-off" partner for "those carnival images of celebrity death". Quite; I remember being shocked by those photographs.

In a brief space, David Rieff marries the detail of illness and death with an abstract consideration of the way in which both are handled today, especially by those who are professionally involved.

He writes with elegance and high intelligence; the book is a fine epitaph to his mother.

Penelope Lively's most recent novel 'Consequences' is now out in paperback (Penguin)