Most Helpful Guy
To put it as simply as I can... cancer is any unregulated cell growth. It can spread from region to region, and one of the ways it spreads is via the lymphatic system, which can be thought of as the bodys motorway system for cancers.
Stage 1 cancer is typically localised in an area. e.g. Breast, liver, brain, etc...
Stage 2 is when the cancer has begun to spread locally, via the lymphatic system.
Stage 3 is when the cancer is now advanced in multiple regions
Stage 4 is when the cancer has infected the lymphatic system itself and is widespread.
Now, all of that is wrong in detail but it's the best and simplest overview I can give you. In actuality, stages are specific for each type of cancer, and some don't even have staging systems.
For most cancers, Stage 4 is usually terminal. Depending on the type of cancer your friend has, the odds of your friend getting better are less than 1%. His five year survival probability can range anywhere from 4% to 90%, but actually getting better and going into full remission is extremely rare.
If I'm correct in assuming that what you call lymphatic cancer, I would know as Hodgekins disease then there's potentially good news. Hodgekins has a 10 year overall survival rate of 90% at *any* stage of its progression. Some patients, with treatment can live between 25-40 years.
There is another class of cancers, though, called Non-Hodgekins. It's about a dozen or so unrelated cancers that have grouped together simply because they are not the Hodgekins version. Some are relatively tame. Some are extremely lethal. Without knowing the specifics of your friends case, I can't give any more information.
For your friends sake, I think Hodgekins stage 4 is his best hope, for any chance at long term survival.