I had treatment for stage 3 lung cancer with the immunotherapy drug pembrolizumab for 2 years back in 2016 on a clinical trial. I should have been entitled to another 2 years as I had a massive response but was denied further treatment. It came down to this, the drug company wanted to maintain that 24 months was the maximum that anyone ever needed in order to make the treatment affordable on the NHS although NICE admitted that the maximum number of beneficial cycles was unknown. I never had anymore treatment and am still here but was very upset at the time.

Well, I am still here and never received any more than 2 years treatment with pembrolizumab I haven't kept up with the data but there is no doubt that back in 2018 nobody knew what the optimum number of cycles were and that includes the chief medical investigator at Merck who conducted the first clinical trial and on TV in 2019  he said there were still people on it after 7 years. (on the first trials they didn't put a cap on the length of treatment)

I felt the same as your husband at the time and even sought private treatment in Colombia where I thought it might be discounted, (it wasn't so I didn't go ahead)

The only way to get more infusuions is if you have private  health insurance or can afford it as far as I know but as I said I don't keep up the latest data. Good luck to your husband it worked for me and hopfully it has done the job for him.