The lives of a breast-cancer patient and a researcher who is trying to prove a genetic link to cancer intersect in a groundbreaking study.
| Actor | Role |
|---|---|
 Samantha MortonAnnie Parker | Annie Parker |
 Helen HuntMary-Claire King | Mary-Claire King |
 Aaron PaulPaul | Paul |
 Alice EveLouise | Louise |
 Maggie GraceSarah | Sarah |
 Rashida JonesKim | Kim |
 Corey StollSean | Sean |
 Richard SchiffMr. Allen | Mr. Allen |
 Bradley WhitfordMarshall | Marshall |
 Marley SheltonJoan | Joan |
 Ben McKenzieTom | Tom |
 James TupperSteve | Steve |
 Robert PineDr. Frank | Dr. Frank |
 Bob GuntonDr. Benton | Dr. Benton |
 Chris MulkeyRalph Parker | Ralph Parker |
 Chad LindbergFuneral Home Employee | Funeral Home Employee |
 Benjamin StockhamYoung William (Age 8) | Young William (Age 8) |
 Ryan WynottYoung William (Age 12) | Young William (Age 12) |
| JJade DuncanYoung Annie Parker | Young Annie Parker |
 Olivia Rose KeeganYoung Joan Parker | Young Joan Parker |