My friend has had surgery for colon cancer but has been told she possibly has another 5cm tumour attached to the aorta.... can this be removed too?

Probably not: If this is "adenocarcinoma of the colon", then the tumor next to the aorta represents growth outside the wall of the colon, which means it isn't possible to cure this with surgery. However, it is important to confirm that the mass is a recurrence or extension of the primary colon cancer. If so, then radiation and chemotherapy can help, but are not likely to cure the cancer.