C-

And you thought “The Notebook” was shamelessly manipulative. Nick Cassavetes outdoes his previous tearjerker with this two-hour dirge about a young girl dying of cancer. Like a Lifetime disease-of-the-week movie on steroids, “My Sister’s Keeper” tugs at your heartstrings so relentlessly that by the time it’s over you might require a defibrillator.

The girl in question is Kate Fitzgerald (Sofia Vassilieva), who’s diagnosed with leukemia as a child and survives into her teen years as a result of a controversial decision taken by her parents Sara (Cameron Diaz) and Brian (Jason Patric) to use in vitro fertilization to have another child that will be a genetic match for Kate and so serve as a source of blood, marrow and even organs as needed. That turns out to be Anna (Abigail Breslin), who’s willingly met her older sister’s needs for a decade but now, at age eleven, provides the dramatic (or melodramatic) crux of the narrative when she hires lawyer Campbell Alexander (Alec Baldwin) to sue for medical emancipation when Kate needs a kidney transplant.

The decision makes “My Sister’s Keeper” part courtroom drama as the case is taken up before a female judge (Joan Cusack), but the emphasis remains on the Fitzgerald family dynamic, with the focus not just on Kate and Anna, but Sara, who’s put her own life on hold for her ill daughter—she was a lawyer herself, but abandoned her job to do everything in her power to keep Kate alive (and enlisted her sister Kelly, played by Heather Wahlquist, as essentially a full-time caregiver). Sara comes out of retirement to face off against Scott and retain her right to decide that Anna will donate one of her kidneys to save Kate’s life.

The idea of a young woman facing death can’t help but be compelling in a way, but Cassavetes and his writing collaborator Jeremy Leven, working from a novel by Jodi Picoult, aren’t satisfied with telling the story cleanly and straightforwardly. They’ve instead adopted a puzzle-like script structure that not only tells the story from the shifting perspectives of individual characters (though on close inspection it’s a technique they ignore as often as they follow it) but toys with the chronology, tossing in flashbacks with abandon to flesh out the past. The result is often a jumble.

In addition, they ratchet up the mawkish quotient mercilessly. It’s not simply that they go for the jugular in sequences like the inevitable one where Kate wants to make one last visit to the beach, even though it might endanger her fragile condition, or that they overplay Sara’s mother-lion quality, to the detriment of Diaz’s performance (she comes across entirely too shrill and controlling). It’s that they (or Picoult) ladle on the tear-inducing elements in such grotesque profusion. So not only do we get a subplot about a tender romance between Kate and a fellow cancer patient, Taylor Ambrose (Thomas Dekker), which includes a prom sequence and the obligatory sad follow-up. It also turns out that the judge is just back from a sabbatical following her own young daughter’s accidental death—a circumstance that requires Cusack to scrunch up her face gruesomely in a portrait of perpetual motherly pain. Even Baldwin, who mostly brings a rare touch of light humor to the picture in his early scenes as a guy who’s advertised his way to commercial notoriety, is turned into a maudlin figure in the last reel; he has a medical secret of his own.

Even within this universe of misery, Vassilieva remains the real star of the picture, capturing Kate’s anger and depression over her condition as well as acing the sequences that grimly portray her infirmity; it’s hard to retain one’s dignity in playing such a character under heavy-handed direction like Cassavetes’, but she manages to do so. By contrast the better-known Breslin, while spunkily effective, makes far less of an impression.

One of the curiosities of the picture is that despite its emphasis on the female characters, you might actually find yourself feeling especially sympathetic to the guys—to Brian, whom Patric limns as a decent fellow pushed around by his wife, and to the Fitzgerald’s middle child, son Jesse (Evan Ellingson), who becomes the forgotten member of the family unit, so much ignored by his parents in their concern for the daughters that they don’t even notice that he has a learning disability or that he often goes off at night to wander the streets of Los Angeles alone (in some of these scenes, you worry that the kid’s going to be picked up by someone unsavory). Jesse has to carry some pretty heavy emotional baggage, and Ellingson plays him well, giving the character a touch of subtlety lacking in most of the others.

“My Sister’s Keeper” is visually proficient, with Caleb Deschanel’s cinematography avoiding the glossy look of an old Ross Hunter weepie. But the score by Aaron Zigman strikes the predictably mournful notes, merely accentuating the fact that the picture italicizes the sadness in a fashion that cheapens the narrative (as does the “twist” but unsurprising ending). The only blessing is that we’re not told at the beginning that the movie is based on a true story. Despite the title, this is certainly no keeper.