I afraid there's not much you can do, mainly just being there helping if there is something you can help with. But being there in case they need support or some one to talk to. 

Billy 

Hi.  Is it a work colleague?  My mum was diagnosed with terminal cancer in January and I am accompanying her to all her appointments, treatments and visits.  

I am getting some marvellous support from my manager and the team I work with.  The things that I have found helpful are:

- to identify important work and what can wait

- the chance to avoid difficult meetings and conversations 

- being made aware of the policies and support for carers and compassionate leave

- being allowed to get into work a bit later if I have a poor nights sleep 

In return it is expected that I am totally honest with regards to my needs and any issues that are/may effect my work/attendance.  Sometimes this has been stressful as often I’ve not been able to process events or feelings, but mainly helpful.

Your colleague is very lucky to have you.  I hope that any of the comments above are helpful.