I had heard that you only need to prune off damaged or diseased areas, and around the bottom 12" or so to provide a clear area for ventilation and to avoid splashing contamination from the soil (if you're not mulching). And certain branches if they're in an inconvenient place.

Some tomato varieties like to have their extra suckers removed, others don't.

Otherwise, if it's doing well, you might want to just let it continue growing. I have never heard that hard pruning is of value to tomatoes.

Sue

When I lived in So Cal I would occasionally some across what I called "tomato trees" -- old abandoned veterans. The fruit was usually not very good. I had the same problem with my own tomato plants come November or so... the fruit quality was just declined after a while. So I usually let the tomatoes reseed themselves and chopped off the parent plant at the stalk when the younglings needed room and sun.

But if your fruit is still tasty, I can't think of any reason to prune the plants.