Dewberry, 34, who won the second series of the BBC show in 2006, told Twitter followers she had cancer following a biopsy.
"Biopsy results received. Turns out that what I thought was a persistent pimple on my face is actually skin cancer," she wrote.
"Thx for your messages guys. I'm gonna be just fine. Op booked in to cut it out. Just wanted to share, to encourage others to get checked too."
The former supermarket checkout girl, who left school with only two GCSEs, beat rival Ruth Badger to win the second series of The Apprentice. Dewberry, from Hull, who was running her own telecoms business by the age of 24, worked for Sir Alan Sugar for 11 months, taking a £100,000-a-year job as head of Xenon Green.
She became pregnant with fellow contestant Syed Ahmed's baby, but suffered a miscarriage.