@cindylb- How awful for you and your husband to endure so much and how frustrating it must be not to know what type of cancer your husband has. I agree with @burrkay about asking your husband's doctor about a molecular study for the purposes that he stated. Believe it or not it's not common not to be able to identify where the cancer started but it does happen. And often times with advanced cancers the origin of the cancer is never found because the cancer cells are poorly differentiated (haven't matured enough to be identified). Parts of my first cancer were poorly differentiated. Andhttps://www.cancerresearchuk.org/about-cancer/cancer-unknown-primary-cup/about sometimes the original cancer is fought off but a secondary one forms in the lymph system.
@ina3 and her dad have been struggling with a similar situation and perhaps she will chime in here., especially the discussion she is having with @colleenyoung on Feb 26, this year. You can also check out her posts.
Have you considered having his biopsies looked at by another lab?