NEW YORK -- "Good Morning America" host Robin Roberts announced Tuesday that she has breast cancer.

Roberts will have surgery Friday and immediately begin treatment.

"I am blessed and thankful I found it early," Roberts said.

She made the surprising announcement with GMA co-host Diane Sawyer by her side, saying she wanted everyone to hear it from her.

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Roberts said she discovered the lump the day they did the tribute show for Joel Siegel. He died of complications from colon cancer on June 29.

Roberts had done a story on the importance of early detection.

She contacted her doctor, who told her to have a mammogram and an ultrasound. She said the cancer was not detected in the mammogram, but the ultrasound found it.

"Once you are diagnosed, you are a survivor," Roberts said.

Sawyer said that 250,000 women every year are diagnosed with breast cancer, and 80 percent who get it have no family history of the disease.

Roberts said there is no history of breast cancer in her family.

"I will get up every morning and say, 'Good Morning America.' I will have good days and bad days," she said.

Written Statement

Roberts released this written statement Tuesday morning announcing her breast cancer diagnosis:

I never thought I'd be writing this... I have breast cancer.

It all started a few weeks ago. We had gotten the news that our dear colleague and friend Joel Siegel had passed away and we began preparing for our special tribute show for him.

I did a piece about Joel's courageous battle with cancer, reporting on the way my friend had lived his life and been such a successful advocate for the importance of early cancer screenings. That very night when I went to bed, I did a self breast exam and found something that women everywhere fear: I found a lump.

At first I thought, "This can't be. I am a young, healthy woman." Nevertheless, I faced my fear head on and made an appointment to see the doctor.

Much as I was hoping the doctor would say it was nothing, she did a biopsy and confirmed that the lump I'd found was indeed an early form of breast cancer.

Hearing the doctor say those words out loud was surreal.

I will be having surgery shortly and follow-up treatment in the months to come. So in the coming months, you will probably notice that I will have my good days and my bad days, but I know I will get through it with the love and support of my family and friends. Diane, Sam, Chris and all of the folks behind the scenes who make this program come to life each and every morning have been so supportive and loving at this challenging time.

To you, our viewers, please know that your thoughts and prayers very much sustain me as they always have each and every morning when I sit in the chair next to Diane and say "Good Morning America." You have always been there for me ... and I love you back.

And like my good friend Joel, I can't stress enough how important it is to get screened and checked for all cancers -- and to do self breast exams. I am so blessed that I found this in the early stages and the prognosis is so promising that my doctor expects me to be flying planes and hanging on to submarines in the middle of the Atlantic and scaling the Mayan Pyramids in no time in the mornings to come.

Now I join the ranks of millions of Americans who are fighting this same battle each and every day. I appreciate YOUR courage and YOUR example. Thank you for showing me the way.