Confused

My husband was diagnosed with stage 3 esophageal cancer. He was in the navy in his 20s, he's 52 now. He had never signed up for the VA until the diagnosis. When we went to his first doctors appointment, the person that helped us make our new appointment said that he should go make a claim with the VSO i think that's what they were called. The man we saw seemed pretty sure my husband would get 100% disability while going through chemo, radiation and surgery. He was in the places on the list for exposure presumptive list. He is an over the road trucker right now and will have to take off at least 3 months. Does this sound like he will get it? And does a doctor have to say that it's service related?