Laura Linney's third role in which her character is diagnosed with terminal cancer.
Sean was originally a 26-year old, but Laura Linney offered the role to John Benjamin Hickey and the character was rewritten as the slightly older brother.
John Benjamin Hickey was nominated for a 2013 Primetime Emmy Award in the Outstanding Supporting Actor in a Miniseries or a Movie category for his role as Sean Tolkey.
Bill Condon (director of the pilot) and Laura Linney have been friends and have worked together for years.
The title of this show was originally "The C-Word," and some promotional materials were made using this title. But while a guest on "The Daily Show," Laura Linney told Jon Stewart that the title was changed from "The C-Word" to "The Big C" to avoid confusion with L Word (2004), which had also aired on Showtime.