From PEOPLE Magazine Click to enlarge
For Katie Couric, the fight against cancer is a deeply personal cause: In 1998, the CBS Evening News anchor lost her husband, Jay Monahan, to colon cancer, and in 2001 her sister Emily died of pancreatic cancer. Long a devoted activist, Couric cofounded the National Colorectal Cancer Research Alliance (NCCRA) and famously underwent a colonoscopy on the Today show. Recently, she helped develop the idea for Stand Up to Cancer, a star-studded fund-raising special airing Sept. 5 on NBC, CBS and ABC. Couric, 51, spoke to PEOPLE's K.C. Baker about the emotional toll cancer has taken on her and her daughters Ellie, 17, and Carrie, 12. "I hope that collectively we can change the face of cancer forever," she says.

How has cancer changed your life?

It completely destroyed my family twice. My husband, Jay, died when he was 42 and our daughters were 6 and 2. My dream to have a happy, intact family was completely obliterated. Three years after that, my sister Emily was diagnosed with metastatic pancreatic cancer.

How did you get through that painful time?
I knew I had to continue to be there for my kids. They were so little. When my sister was diagnosed, I had to be there for my parents. I also have wonderful friends who all loved Jay. When you lose someone and are surrounded by people who cared about that person as much, it's helpful. And I got thousands of letters from everyone from John F. Kennedy Jr. to President Clinton to people who watched the Today show.

How did you help your kids get through it?
A certain amount of honesty. If Ellie would ask me if her dad was going to die, I would say, "I hope not. I know the doctors are doing everything they can to help him." I tried not to create unrealistic expectations. I did worry for a time that my kids would think everybody got cancer. They learned a lot from my campaigns. I don't think they are fearful.

Your work with the NCCRA and your on-air colonoscopy helped a lot of people learn more about cancer.
People used to write to me that when their doctors asked them who referred them, they would say, "Katie Couric." And these doctors would be like, "What?" I think it got through to a lot of people. Believe me, I didn't think it would be a ratings booster!

Why is raising money for cancer research so important now?
We are right on the cusp of so many discoveries and approaches. These scientists need funding. And I hope it will empower people—when I saw Jay and Emily going through this I felt so powerless. I hope that people feel that they can make a difference even if it means calling in $5 or going to www.standup2cancer.org and buying a star for $1 in honor of a loved one. We bought a star for Emily and Jay.

How do you keep Jay's memory alive for Ellie and Carrie?
He comes up in conversation a lot. The girls may do something, and I'll say, "Your dad did this too." My children have lived longer without their dad than they have with him. But that doesn't mean we don't miss him every day. I often think, "He would be so proud of them."

Your daughters have a lot to be proud of when it comes to you too.

I remember when Ellie was 9, and she looked at me in the kitchen one day and said, "I'm so proud of the work you've done helping others." I was touched by that. They were very upset when they learned that Christina Applegate was recently diagnosed with breast cancer. They said, "She's so young." I told them that her prognosis was great.

Who are they excited to see on the special?
Rihanna. They know that I love her and they like her too. They love Beyoncé. They're excited about the stars—and they think it's a great cause.

For more information, go to www.standup2cancer.org