A mother’s obsessive love for her cancer-stricken teenage daughter at the expense of her family sparks friction, sending her 11-year-old daughter to a lawyer to sue to get out from her mother’s control in My Sister’s Keeper.

One of the most unusual films of the year, My Sister’s Keeper tackles such heady themes as death, loyalty, devotion and refusing to let go … while trying to be entertaining. That’s not easy for a film that spares little in showing us the suffering endured by 16-year-old Kate Fitzgerald (Sofia Vassilieva of TV’s Medium) as she faces her final battle with the disease. But director Nick Cassavetes (who co-wrote the screenplay with Jeremy Leven from the novel by Jodi Picoult) knows his way around such delicate subjects. He directed the tearjerker hit The Notebook (whose script was written by Leven) and mostly succeeds thanks to a powerhouse cast in top form.

Cameron Diaz goes against type — looking frazzled, worn and desperate through most of the film — as the mother who refuses to accept the fact that her daughter is dying, trying by every means to find some miracle cure. This involves the involuntary participation of Sara’s 11-year-old daughter, Anna (Abigail Breslin), who we learn from Anna’s narration at the start of the film was genetically engineered to have the same makeup as Kate so she could later serve as a “spare parts” warehouse for her sister. Since she was 5 Anna has undergone various painful procedures, including a bone marrow transplant, to be used to save Kate, who has a rare form of leukemia. Now Kate’s kidneys are failing and Sara wants to remove one of Anna’s kidneys to save Kate again. But Anna balks at the idea. She seeks help from hot-shot lawyer Campbell Alexander (Alec Baldwin), asking him to bring suit against her parents for the right to control her own body. She wants, she says, to have a normal life.

This shocks Sara, sending her into defense mode as she tries to pressure Anna into changing her mind. A former lawyer who has given up her practice so she can stay home and care for Kate, Sara decides to challenge her daughter in court. Diaz plays Sara like a tigress protecting her cub. She has given up her life for Kate, even letting her marriage slowly fall apart in the pursuit of what has become a full-time occupation. Sara’s refusal to accept the inevitable and her blind devotion, which has become her only passion, make her more than a little obsessively nutty.

Her husband, Brian (Jason Patric), tries to be understanding to both his daughters and to his wife. But Sara has driven a blind-sided wedge between them that’s even affecting son Jesse (Evan Ellingson), who we see is having emotional problems that his parents are not aware of. That Diaz manages to create in this highly motivated, fixated character a note of sympathy is a remarkable feat. She is, for most of the film, as appealing as the Wicked Witch of the West. But her eventual acceptance of the truth pays off in a teary moment of understanding that’s emotionally charged.

Throughout My Sister’s Keeper Cassavetes employs flashbacks to explain how the whole idea of creating Anna to save her sister came about, as well as to show that Kate has not always been a bedridden recluse. In one amusing scene Sara shaves her head bald so Kate, who has lost her hair from radiation therapy, won’t feel like a lone ugly duckling. Then the family goes to a photo booth for pictures of the hairless results.

Later there’s a lovely sequence as Kate discovers her first romance with a young man she meets while they are both undergoing chemotherapy. The scenes in which they attend a dance for patients at their hospital is played to underscore the sense of magic and romance. Vassilieva makes a radiant showing here, counterbalanced with contemporary scenes in which Kate maintains her composure and clearheaded thinking while suffering the ravages of the disease. In melancholy scenes we see that Kate has taken a pragmatic approach to the cancer that is killing her and guilty feelings that her mother has given up her own work and life to fight her battles.

Cassavetes has created a strong ensemble cast that plays off each other with precision to bring the film to life. Breslin may seem a little callous at first in the way she announces her decision to sue her parents with cool, matter-of-fact practicality. When her lawyer asks Anna if she realizes what will happen to Kate if she doesn’t get a kidney, Anna replies unemotionally that she “will die.” Only later do we discover that there’s an underlying purpose to her decision and we see the easy sisterly devotion shared between the girls.

Baldwin is especially good as Alexander, a lawyer who brags in his TV commercials that he has won 90 percent of his cases. At first he is bemused by Anna, yet he treats her with respect as a client and rallies to her cause, especially when he sees the groundbreaking implications of her case, something that appeals to his sense of what is right for this child.

Good, too, are Joan Cusack as the presiding judge who is also trying to overcome a recent tragedy in her own life; Patric as the father, a decent man who has lost control of his family but tries, in a very surprising moment late in the film, to win back what had been lost; Ellingson as the son whose own growing pains, coupled with being pulled every which way by a dysfunctional family, leave him an emotional wreck.

My Sister’s Keeper is not an easy film. It’s certainly contrived. Could something like this really happen? And Cassavetes is often manipulative to wring out the tears, keying up the sad music following a death as the survivors share their sorrow while rain runs down the window behind them. Yet the film is riveting and, in an odd way, life affirming with a sense of hope. And that’s all these people have to go on.

****My Sister’s Keeper

Starring: Cameron Diaz, Abigail Breslin, Alec Baldwin, Jason Patric, Sofia Vassilieva, Joan Cusack, Evan Ellingson.

Rated: PG-13, contains adult themes, sensuality, disturbing images, profanity.

mjanuson@projo.com