The E! News host made the announcement during an appearance on NBC's Today Show this morning.
Giuliana, who is married to businessman Bill Rancic, discovered she had a tumour while undergoing in-vitro fertilisation in a bid to get pregnant.
However, doctors are optimistic they detected the cancer early and the 37-year-old will make a full recovery.
Kelly, 26, whose mum Sharon was diagnosed with colon cancer in 2002, took to her Twitter page today to let Rancic know she is thinking about her during this difficult time.
She wrote: 'I just want u 2 know I love you & that I'm thinking of u! u r a strong women & ur going 2 beat the s*** out of this cancer!!!'