Pancreatic cancer for 6 years: Afraid of running out of chemo options

My husband has had pancreatic cancer for 6years. He has had theee different sets of chemo. He had a tumor come back on his back and later one outside his stomach. He underwent radiation for both of these. They were timy tumors. They do a CA19 blood test every 4 weeks and a Ct every three months. Recently he has a small tumor less than a pea size in his lung. They have switched his chemo again. He will be having a scan in January. My question is has anyone had a tumor in the lung shrink or go away after doing chemo? I’m afraid we are running out of chemo regimens. I feel he has been on all the drugs.