Definitions, screening and treatment of cancer are constantly evolving. Photo credit: Getty Images.

There are more than 12 million cancer survivors in this country, according to the American Cancer Society. This year, there will be 1.6 million new cases of cancer diagnosed.

Join us as we talk to experts from the American Cancer Society, National Cancer Institute and other expert groups on today's ABC Health Tweet chat.

You can follow the full chat on Twitter. Click here for details.

Or follow the highlights in the live blog below. For mobile readers click here.