She has dedicated her life's work to shocking the world with her exploration of the relationship between the body and language. But even she was surprised when she found she had cancer and her body started telling a story of its own
Kathy Acker's body doesn't belong to her. It isn't the body of a 50-year-old woman but of an adolescent boy. It isn't private and hidden, but public property, part of her life's work, which has been to explore the relationship between the body and language, text and flesh, discourse and skin. This month sees the publication of two new collections of her writing: Bodies of Work, a series of critical essays on subjects from art to science fiction and Burroughs to de Sade, and Euridice in the Underworld, a collection of short stories.

Her writing on the body extends to a physical marking of her own body; she has shaped it with weights, coloured it with needles and ink and distorted her appearance by piercing her flesh with lumps of metal. She has re-made herself physically just as she has reinvented her self intellectually, from undergraduate punk poet to university lecturer and from illegitimate New York Jew to hippy to post-modernist, novelist, art critic and performance artist.

Acker is not pleased with her current appearance, although, at 50, she looks younger than in the famous photograph of her on the wall behind her head, where, captured by Robert Mapplethorpe in her twenties, she looks less wide-eyed and more curvaceous. She likes her hair, which she has recently dyed black and clipped into zigzags, but she thinks she looks like a "skinny rat". The weight has been falling off her since she mistook a bottle of dirty river water for Evian with gutwrenching consequences.

As she scurries around her north London basement flat, a dark and cramped warren of narrow corridors and low-ceilinged rooms, she has a curiously rodent-like quality. Her wide eyes, blinking heavily in the lamplight, her sly sense of humour, her sudden movements all point to an underground existence. But then Acker has lived her life, figuratively if not literally, underground; at the edge of US and now British counter-culture.

Take Pussy, King of the Pirates, a radical re-working of Treasure Island deemed unsuitable for publication as a novel in Britain ("It's the hardcore girl-sex, I think"). Acker puts on a crackling recording of a musical version she is currently performing with punk band The Mekons. It is mainly girls swearing in angry sing-song over a thrash/disco soundtrack. Acker relishes swearing. She enjoys the word "cunt". She also enjoys the prefix "post" - structuralist, modernist, feminist - which she scatters liberally through her speech like a sort of pretentious glitter.

At 50, her desire to shock is undiminished. She has recently had her labia pierced, she says matter-of-factly, and she has been coming at random, in theatres, cafes and, probably, interviews, ever since. She can't get by without plenty of sex, she says, mostly with men, sometimes with women. Her fascination with body-piercing - eyebrows, belly button, etc - began in her mid-forties. At 30, it was body building; not just a few weights in the gym to fight the flab, but serious muscle-building. At 40, around the time she published Blood and Guts in High School to critical acclaim, it was tattoos, of flowers and birds and cats. It was all - even a tooth, banged out by accident and then left badly patched up at the front of her mouth - part of the project. "Ageing frees you," says Acker. "After a certain age in America, particularly if you are not part of a recognisable couple, whether lesbian or straight, women become invisible. I found there was no need any longer to conform to anybody else's idea of how I should look."

But two years ago, Acker's body suddenly changed all by itself, unscripted. "Oh yes," says Acker. "My body decided to get in on the act in a big way." First it was benign lumps, appearing in her breasts. Then, a malign lump above her heart. The doctors told her it was very serious; that she would die. Acker felt betrayed not by her body, which still felt perfectly healthy, but by medicine. "Okay, so I have always been radical, but, at some level, I always believed the men in the white coats had all the answers," she says. "But they didn't. It was like they had taken all the meaning from my body. I thought: I will not die a meaningless death. I will find out the answers. I will make myself well, or at least I will die in control of my body."

Acker had a double mastectomy, but refused chemotherapy. "I lost a lot of friends," she says. "They couldn't bear to watch me refusing chemo." Instead, she started her own investigations into the cancer. She began, literally, to deconstruct herself. "I looked at everything," she says. "I looked at my diet, pollution, my childhood, my genes, the stress I had been under, my lifestyle. I even examined my past lives."

Her own past was painful to explore. Her biological father left her mother in New York when she was three months pregnant. Her mother was bitter, believing her baby daughter, Kathy, had ruined her life. Then, when Kathy Alexander was 19, she married her best friend, a penniless 17-year- old who she simply calls "Acker", because her mother and stepfather wouldn't pay for her to go to college. As a married woman, she was eligible for a scholarship to Brandise.

Years later, she married again, this time Peter Gordon, a man she says she loved. "After we married, it went wrong. We became jealous of each other, encroached on each other's space." She is still one of love's fools, she says, surveying the boxes of books littering her flat, packed up and waiting for the ship to take them home. She came to London a year ago, for love, for a man she thought she might settle down with. "It's over," she says. "I've been a fool and now I'm going home to California to live in the woods."

But then, she is different now, at 50, to the Kathy Acker who, at 48, fell in love and found she had cancer. In taking herself apart, in confronting the ghosts of her dead parents and the friends she lost to Aids and heroin, in finding what she was made of psychically and physically, she found all the answers, she says. "I understood how things had combined to make me sick." Then she set about putting herself back together again, differently, in a way that would make her well. "And I am well," she says. "I've had the all-clear from the doctors. I'm no longer dying and I can't tell you how happy I am just to still be alive."

Her breasts, even, are growing back, "like a young girl's". She feels renewed, invigorated, born again. Being Kathy Acker, she is now considering having nipples tattooed onto her flesh. And her next project is to sit down and write about the cancer and how her body, for once, constructed a narrative of its own.

'Bodies of Work' is published on 20 September by Serpent's Tail (pounds 11). 'Euridice in the Underworld' is published on 29 September by Arcadia (pounds 10.99).