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The true story of American geneticist Mary-Claire King (Helen Hunt), and the friendship she forged with breast-cancer patient Annie Parker (Samantha Morton) while searching for the link between DNA and cancer. Parker was just 11 when she lost her mother to breast cancer. Seven years later, her father has passed away as well. Married to Paul (Aaron Paul) at 19, Annie is expecting her first child when her older sister, too, succumbs to the same disease that claimed their mother. Meanwhile, esteemed research scientist King is on the verge of a scientific breakthrough that could revolutionize cancer treatment and perhaps save Parker's life. But first King must convince her skeptical colleagues that some individuals are genetically predisposed to cancer -- a theory that's been largely rejected by the scientific community. Later, as an optimistic Parker fights to remain brave for the sake of her young son, the two women find their fates intertwined, and King makes a discovery that will forever alter the way that cancer is diagnosed and treated.