Hello @frankbc - My name is Cindy Bond and Colleen Young tagged me on your last post because your husband has a 'cancer of unknown primary' and so does my husband. It can be a very difficult situation because you can't a clear protocol to follow from the doctors and it doubles the unknowns you face with cancer. My husband's cancer is still unknown but leaning lung cancer. None of the biopsies showed a clear diagnosis. He waited just short of three years for any treatment because oddly, the cancer (a Stage IV) was spreading in his bloodstream but the only tumor was in his lung and a nearby lymph node and wasn't growing, until recently. His biopsies showed elements of lung and upper GI cancer. After PET Scans every three months for 3 years with no growth, the cancer suddenly grew very quickly and aggressively to his bones and in the lung area and center of his chest. From that information we were able to move forward with a chemo and immunotherapy plan of Carboplatin, Alimpta and Keytruda. My husband had "Foundation Testing" which showed a very small amount of PDL-1, which might mean lung and which Keytruda works to remove, but we still don't know for sure what cancer we're dealing with. My husband just finished his four major treatments and will now move to 'maintenance therapy' of Alimpta (a chemo drug) and Keytruda. That might tell us more about a definitive diagnosis (we can hope) because the Carboplatin chemo is very strong and pretty much kills every cell, so I believe it would work well on many cancers. Same with the Alimpta I think, but the Keytruda only works on select cancers. Four sessions of chemo/immuno has eradicated the cancer in his bones, almost all of the lymph node cancer is gone and the tumor in his lung has reduced by half or more. It is our hope that the maintenance will keep it at bay but the doctors aren't really looking for a 'cure' for my husband as much as increasing the number of months/years he has. We are of course hoping for more but understanding that might not be the case. My husband had considerable and some severe side effects from the chemo. We don't know, given there were three drugs in play, which caused the major side effects but probably the Carboplatin. We're hopeful the maintenance will be kinder to him and yet keep the cancer from growing again. Also, my husband had 5 sessions/treatments with radiation to the center lymph node and that may have helped that area a great deal. I hope our situation might give you a little more information on another patient facing an unknown primary. If you'd like to stay in touch I'd be happy to do that and also hear about your journey and results. p.s. I'm also a breast cancer survivor - five years in November!! So, I've spent lots of time researching cancer. Just enough to be a pain in the....you know what.....to our doctors, ha ha. Hugs to you and your husband.