How bloody scary is that! Am thinking about you this morning as you head in for that biopsy.
I truly hope that your 'lit up' higher lymph nodes are just inflamed because they are doing the work of being lymph nodes, and nothing more than that. Try not to look at 'what next' until you have the results of the biopsy, particularly as you (say you) haven't had any symptoms. PET scans can be be just too good sometimes, and picking something up on scan doesnt necessarily equate to your worst case scenario. It tells you there's something going on but not what it is.
If it turns out that the results confirm lung metastases - and you aren't there yet - (I'm also assuming that you are based in the U.K.) I can only suggest checking out the Cancer Research UK site and checking their search tools for recruitment criterion in current clinical trials. Immunotherapy drugs are increasingly being included in trials, but inclusion/exclusion criteria will be stated too. Check the trial 'centre' as well, sometimes the treatment can only be given in Manchester or London or something, so you'd need to be sure you could get there for each treatment cycle & check ups which could be time consuming & expensive. If you see a trial that might work, you could put that in front of your Consultant and ask to be proposed for recruitment to it. That still won't mean you are on the trial, but the trial centre team can consider your individual circumstances & perhaps even examine you/run some tests, alongside your existing team.
You could also ask to have access to the Stage 4/palliative section of this site. I'm sure there will be ladies here who have been through this, explored drug trial options, perhaps even been on them and who can offer really practical useful advise and psychological support strategies for dealing with this.
Finally, I'm selfishly thinking about my own circumstances in response to your post. I had a clear MRI in April, and although I have physical (including vaginal & cervical examination) check ups at the Oncology clinic every three months, my next MRI Scan isn't due until April 2018. I feel OK, but I had spread to my para aortic lymph node before initial treatment, so I do worry about spread to my lungs and elsewhere in my abdomen & pelvis. It's a rational fear given my initial diagnosis, but one I mostly manage to keep in check. I have huge confidence in my Oncology team who are based in a big Oncology Centre and they've promised to rescan earlier if there's any suspicious symptoms, so I have to trust that process but god it's hard when I see a post like this. I'm totally rooting for you on this.
A big virtual hug coming from me to you right now.