Has anyone got pregnant whilst partner is having cancer treatment?

I've just found out I'm 5 weeks pregnant, it's come as a complete shock, I was sure my partner wasn't able to have any more children! I would love to keep the baby but we've been told before, when he was on different treatment not to conceive. This time round he's having something called immunotherapy, and his new doctor hasn't mentioned us having to avoid a pregnancy. I just don't know what to do, I'm anxious that I may have a poorly baby and my doctor gave me little advice. If anyone has a similar story, I would love to hear it!