Hello James... Well this is encouraging news. I'm not sure how doctors approach diagnosing over there, but my experience here in the U.S. is that the CT scans and MRI's are an invaluable tool to locate a mass, tumor, or any other solid irregularity. It doesn't tell the doctor what it is as far as cell type. An experienced doctor may highly suspect cancer based on appearance, shape, size, etc. but the confirmation comes from the pathology report of a biopsied tissue sample.
I do hope in your Mum's case they are correct in saying the liver cysts are benign. I have had small liver cysts for several years now and multiple doctors have noted it and said they are "benign cysts" and are of little concern. I have to confess, it does worry me at times due to having had bladder cancer as well.
Below is the mention of it on my latest CT report. I have been scanned yearly now 4 times. As long as it says "unchanged", I suppose I will try not to worry about it further.
"Multiple cystic structures in the liver remain unchanged. Dominant cystic structure in the right lobe of the liver measures 1.4 cm."
I hope they confirm that your Mum does not have mets and can then concentrate on TCC diagnosis and treatment. My best to you both... Your Mum and I are about the same age.