I am sorry for what you are facing- I too was metastatic G10 (nodes only) on diagnosis, just one year earlier. I can offer only my opinions based on therapy experiences I have had for the past two years- and of course my earnest wishes for a homerun therapy in your future.
First, I hope Steve is mostly asymptomatic and pain-free at this point, suffering only the side effects of ADT. Increasing PSA on Zytiga suggests castrate-resistance, but still in the early stages. As Tall Allen said, Provenge is a likely next therapy- some suggestion in the literature that it will be more effective in the earlier stages of CRPC, so I encourage you to require that treatment from your team ASAP. In my opinion, this option should have been presented to you already with PSA of 10 and rising on Zytiga(cranky old men seem to have a lot of opinions, eh?)
Second, you need to gain access to a tumor to obtain DNA sequencing through the Foundation CDx product (FDA approved for analysis of any solid tumor)- with only nodes affected this can be problematic, although there may be ways to get circulating tumor cells from the blood for analysis. Bring this up with your team (my MO and I have been waiting to get at a solid tumor; recent hematuria was due to tumor recurrence in the prostatic urethra, removed by TURP and now available for DNA analysis)- Certain genetic signatures will suggest new therapies, particularly mutations in DNA-repair genes and MSI-H status (microsatellite-instability high: an indication that the tumor cells make LOTS of mutated proteins, presenting them on the cell surface, something that KEYTRUDA seems to work well on with FDA blessing as well); you may be deemed suitable for PARP inhibitor therapy as well, which you can access in clinical trials, some in combination with KEYTRUDA-like therapies. Some people have hit the homerun with KEYTRUDA.
Third, try to estimate your PSA doubling time right now on Zytiga- if it is around 3-4 weeks, well things are more urgent- if it is > 3 months, you can be more deliberate in selecting a next therapy- I say this only because there might be therapy options to explore IF you are still early and asymptomatic, but the shorter doubling time can close that window pretty fast.
Fourth, and I say this only because of my experiences with this therapy, which is still in trial, read up on Bipolar Androgen Therapy (BAT). I chose to try this with the support of my MO, and not in a clinical trial context- some people can have really good responses to this treatment, others not, we really do not know the parameters for that. Some people can have an exacerbation of their condition- Dr. Sam Denmeade at JHU is running most of the trials for this therapy right now, there is a great webinar (February 2017) on the internet you can find by search. Did it help me? When I started the BAT, my PSA was 2.5 with a doubling time of less than 4 weeks; I had just failed on Xtandi- I am formally off BAT now (radiographic progression), my last PSA was 6; without BAT, assuming steady PSA doubling time, my PSA would be over 160 now. And the last 5-6 months have been mostly glorious as my fatigue melted away. It is scary to consider given the early stage of therapy development, and some might think me unwise to bring it up- but when you are metastatic G10 from the getgo, well you have a different set of considerations before you than most- we are very rare birds.
Last- I remind you to smell the roses. I know it can be hard, I struggle with it often, but it is important to be actively seeking opportunities to enjoy the moment- and let hope find you whenever possible.
my best to you both, be brave and be strong-
3/16 PSA 19.4
Status G10 M1a
5/9 ADT PSA 29.5
PROSTVAC ADT chemo (x4) NADIR .05 10/4
5/1/17 EBRT 37.5 Gy prostate hematuria
PSA 6/27 1.65 off trial -> Provenge
9/19 Xtandi: 0.85; 12/12 Xtandi fail
1/10/18: PSA 2.5 ->BAT; 7/6 off BAT PSA 6.0
6/26 TURP, tumor DNA TBD