Yes, lump found incidentally - was scanned at the time, and they thought just overgrowth of thyroid tissue so opted to wait and watch. Well, they never watched and I didn't get it checked again until several years later after having two children, when I decided that I wanted to make sure there had been no changes. The results were concerning - it no longer just looked like an overgrowth so I had a fine needle aspiration which gave inconclusive results.
When that happens, they recommend surgery - a partial thyroidectory - so they can analyse the growth properly. It turned out to be a cancerous tumour, which I absolutely didn't see coming. Despite being rather neurotic, I totally thought it would be benign, so was in state of shock after the diagnosis... After further scans/check ups, they felt that it had been a very clean removal, and despite originally being told I'd need radioactive iodine treatment and potentially a total thyroidectomy, 10 years later my only further treatment has been a daily dose of levothyroxine to keep my thyroid levels stable.
Looking back, I had various symptoms of a malfunctioning thyroid gland - weakness in limbs and feeling bit crappy a lot of the time. After removal and treatment, I felt loads better and have been totally discharged.
If it is worse case scenario - AND CHANCES ARE IT'S NOT! - it's the most treatable cancer there is.