Thank you for taking the time to respond. This is new navigation for me.
The TERA is confirmed and is not disputed from the VA (and he has established service connection for HTN, DM based on his RVN TERA exposure) but these are relatively low disability ratings since it is his cancer that is the driver of his actual disability. The issue is that colorectal cancer is not yet one of the presumptive conditions related to AO exposure (most other cancers are, and colorectal is a presumptive for burn pits, but not yet for AO). The reason for denial is simply stated as "toxic exposure was 50 years ago, not a presumptive condition". His documentation is clear on the disability caused by his colorectal cancer (all medical records and spousal support letter submitted detailing his ADLs that he is unable to perform, which is unfortunately at this time almost all of them). The dispute from the VA therefore appears to not be with whether or not he is disabled, but with whether or not his AO exposure is likely to have caused his cancer. We have a letter from an oncologist supporting this but I was able to find additional medical journals, prior VA case determinations granting this service connection for other RVN AO exposures, etc supporting the link. I'm just not quite sure how/where to submit this info.
Thank you again.