You did not specify that you only wanted positive replies and I don't believe in giving false hope. I am very sorry for you but my understanding is that the condition is incurable and fatal.
Unfortunately, I don't think there is anything that can be done.
My friend's gelding had suspected Lymphoma in the stomach so it was arranged for him to go into the vets for further tests. Unfortunately he had a massive colic episode a couple of days later and died on the way to the vets.
I know that's not what you want to hear OP, but it is unfortunately the reality of the situation.
I'm so sorry OP and if you have any questions please feel free to pm me. Unfortunately Jamin wasn't diagnosed until already in great pain and colicing. I already knew the outcome before the vet arrived x
I lost my Sidney to it too. We didn't know until the vets found it when he colicked and had to have surgery.
In hindsight the day before the colic episode he bucked me off on the road and bolted home. It was very unlike him and looking back I guess the poor lad was in pain.
I'm sorry to hear this.
Unfortunately the prognosis is extremely poor (in humans the affected part of the gut is cut out and chemotherapy given and treatment is still not successful in all cases). All you can do now is to decide to do the right thing for the horse before the pain gets too bad.