I was going to say what Cheryl said about it may be due to irritation from dip. That in itself is a good reason to quit before it does turn cancerous, which I sincerely hope it is not.

David R. 65 yr old male non-smoker, light drinker, stage 3 or 4, depending on which doc you ask, scc rt. tonsil, 2 nodes, 7 weeks radiation and chemo. No surgery. Teatment ended 3/20/08. PET scan 8/08 showed no cancer.
And now, as of oct, 2010, caregiver to wife, Linda, with breast cancer.
May, 2013, Linda diagnosed with stage 3 ovarian cancer. Enuf already.