Starring Cameron Diaz, Abigail Breslin, and Jason Patric. Rated PG. Opens Friday, June 26.

It’s useless to resist. Here’s a film that centres on a cherubic young teenager with leukemia, for God’s sake, one who smiles sweetly through her pain. And it stars, among others, pretty actors Cameron Diaz and Jason Patric. There are scenes of photo-booth mugging and bittersweet frolicking on a California beach, all set to moody-soulful pop ballads. There’s even an adorable doggie. Yes, unabashed weeper My Sister’s Keeper has that Hollywood sheen—but it’s the unexpectedly piercing realness of this family’s anguish that’s going to get you. Just try to hold back the waterworks.

If you’ve read the source material, Jodi Picoult’s popular 2004 novel, you’ll know the gist. Kate (the affecting Sofia Vassilieva) is diagnosed with cancer as a tot, but neither mommy Sara (Diaz), daddy Brian (played with subtle sweetness by Patric), or brother Jesse (Evan Ellingson) is a match to give her life-saving body bits. Presto! Genetically compatible Anna (Abigail Breslin) is “made in a dish to be spare parts for Kate”.

Fastforward 11 years and Anna, who’s donated everything from cord blood to bone marrow, suddenly refuses to hand over a kidney to save sis. She hires a hucksterish lawyer (Alec Baldwin, hilarious and touching) in order to get medical emancipation. Hell breaks loose.

Except it doesn’t, exactly. Sure, there’s some fascinating legal wrangling (Joan Cusack plays a sorrowfully perceptive, deadpan-witty judge), but this tale by director-cowriter Nick Cassavetes (The Notebook) is more tuned to what’s going down—and breaking down—inside each family member’s head. Ferociously bent on saving her daughter, Sara (a role Diaz sinks her perfect teeth into) can’t see what’s really up with her two other children, her mellower husband, or, significantly, Kate.

My Sister’s Keeper is a blatant heartstring-tugger, sometimes clunkily so, but Cassavetes taps into this family’s exquisitely painful distress with genuine sensitivity. Oh, and the sharp black humour here isn’t the only surprise.