Cervical Cancer

I have just come back from a Colposcopy Appointment at the hospital where i have been told there is a lump and is almost certain its cancer.  

My mind is in over drive and all over the place, how can they tell its "almost certain" its cancer?  

My symptoms all pointed towards peri-menopause due to heavy bleeding but when the nurse came to fit the coil for these symptoms suggest a gynae appointment/investigation which i am grateful for but still confused at the "diagnoses" given today.

I await further tests now which i hope won't take too long in coming through.