The book is called "When Breath Becomes Air." It's a New York Times best-seller. Dr. Lucy Kalanithi said she made sure to get the book published, to fulfill her promise to her husband.
"I think about him all the time and when I look at Cady, she's so beautiful," said Lucy Kalanithi. "She's got these really intense eyes. She's really funny and she's this wonderful kid and some of those traits, they remind me of Paul."
Jennings caught up with Lucy Kalanithi at Stanford Medical Center. She said Paul Kalanithi always loved writing and literature and that helped him as a doctor, and then as a patient.
"He sort of felt literature and medicine were two sides of the same thing. They were like, one makes us human, how do we connect and they each helped him understand life," Lucy Kalanithi said.
Paul Kalanithi was a Stanford neurosurgeon. He was diagnosed with stage four lung cancer at the age of 36. The philosopher side of him led to a powerful New York Times article: "How Long Have I Got Left". And he started a manuscript for a book.
"When I think of him doing chemo, I think about him sitting with a blanket and an IV and his computer, working on writing this and it brings to mind how much he endured physically, so that he could write this book," Lucy Kalanithi said.
Jenning's first met Paul and Lucy Kalanithi in 2014 at Stanford while he was undergoing blood tests. He talked about wrestling with how to live his life with a terminal illness, not knowing when he would die.
"My first thought was that I'd be dead within three months. The first thing I said to Lucy was 'You should definitely remarry and start up a life,' because it this one seemed like it was over," Paul Kalanithi said in 2014.
"It actually felt really loving, like, oh, you just got this terrible news and the first thing you're saying is something about my life," Lucy Kalanithi said.
They decided to have a baby during this difficult time.
"I knew a child would bring joy to the whole family and I couldn't bear to picture Lucy, husbandless and childless after I died," Lucy Kalanithi said, reading from her husband's book.
"He came into the hospital in a wheelchair to see Cady born," Lucy Kalanithi said.
"I hope I'll live long enough that she'll have some memory of me," Lucy Kalanithi said, reading from her husband's book.
Cady was born on the Fourth of July, 2014. Paul died eight months later. He enjoyed every moment with her. Paul Kalanithi's death has been a real struggle for his wife.
"The emotions and the disorientation after somebody dies who is that close to you has been really striking," she said.
The book is dedicated to little Cady, with words that pierce the heart:You filled a dying man's days with a sated joy. A joy unknown to me in all my prior years.
"The main thing is just how much he loved her," Lucy Kalanithi said. "Helping her know that she has a dad and how important she was to him, I would love her to know that."
The Kalanithis were big supporters of campaigns to raise awareness about lung cancer. Lucy Kalanithi still is. For more resources on lung cancer visit the Lung Cancer Foundation and Team Draft.