Does untreated chronic sinusitis cause sinus cancer?

No. But untreated chronic sinusitis can make you feel miserable. It can give you chronic runny nose,reduced smell and pressure like pain.
I think . Given the huge number of people with untreated / untreatable chronic sinus problems, and the extreme rarity of cancer arising at this site, I feel confident answering, "No."
No. Chronic sinusitis if left untreated may cause nasal polyps or other problems. Make an appointment with an Ear, Nose and Throat (ENT) doctor to be assessed and treated.