Bringing Jodi Picoult’s challenging novel to the big screen was always going to be a tough task, but director Nick Cassavetes just about pulls it off.

My Sister’s Keeper is a moral dilemma for the modern age. Sara Fitzgerald (Cameron Diaz) and her husband Brian (Jason Patric) decide to genetically engineer a sibling to be a blood and bone-marrow donor for their sick daughter Kate (Sofia Vassilieva).

After enduring years of painful operations to save her sister, who next needs a kidney transplant, the 11-year-old Anna (Abigail Breslin) takes her parents to court to sue for the rights to her own body.

Kate was diagnosed with leukaemia as a toddler, and her lawyer mum Sara dropped |everything to look after her, never sure when the next nose-bleed might result in a lengthy hospital stint.

She’s clearly a supermum, who almost treats her daughter’s illness as though it’s a courtroom battle to be won.

But Sara’s intense focus on getting Kate better, by any means, takes its toll on the rest of the family, especially when she faces the real lawsuit brought by hotshot lawyer Campbell Alexander (Alec Baldwin).

The complex web of relations between each family member – from the forgotten son Jesse (Evan Ellingson) to the impenetrable bond between Anna and Kate – is handled sensitively, through a series of voiceovers from each actor.

This works, in the main, to give the viewer an insight into each character’s thoughts on the situation, but occasionally these sequences, using music and sometimes grainy flashback shots to set the mood, detract from the action.

Kate’s voice is one of the last to be introduced, but is perhaps the most poignant, as she reveals: “I don’t mind my disease killing me, but it’s killing my family too.” This is the crux of the film.

Despite the ‘happy family’ footage we see at the start, each character is struggling under the weight of Kate’s dwindling life – and no more so than the girl herself.

When Anna files a lawsuit, she claims she wants ‘medical emancipation’ and to keep her kidney for the simple reason that she wants to play sport and eventually have children, but it soon becomes clear there’s another very pressing reason that she’s desperate to hide.

Cassavetes, who won critical acclaim for The Notebook, steers the film just the right side of Hollywood schmaltz with his own brand of naturalism, and manages to keep it light for the most part, despite the heartbreaking story.

Diaz, best known as a comedy actress, gives a competent |performance as Sara, especially in her feisty exchanges with Baldwin, but it’s Breslin who steals the show as Anna, narrating both the opening and closing scenes.

Credit is due to 16-year-old Vassilieva for shaving her head for the entire film – and the most heartfelt scenes are between her and Breslin, who clearly developed a strong sisterly bond off-set to show such unconditional love on screen.

Fans of the book should expect an entirely different ending, and watch out for Baldwin’s ‘service dog’ – a bizarre addition, but one that helps to lighten the mood.