My mother has just been diagnosed with a "circumferential stenosing sigmoid carninoma at the distal sigmoid", which is in her colon.

Does anyone have any knowledge of this?

A biopsy has been taken but the consultant has seemingly  already stated it's cancer, as has the GP. I'm so frightened it'll be inoperable. My mother is 79 but otherwise in very good health. 
Thank you so much 

x