They are mostly benign. I had a baseball sized one removed 6/24/24. Unfortunately, it was Grade 3 malignant, which only 1-3% of them are. Only 300 a year in the USA, so there is very little information about them. I had to follow up with 6 weeks of daily radiation. That ended in September, and now I am on MRI every 4 months to watch for regrowth. I had an MRI this morning, but won't know until next week what the results are. If its relatively small, NS will usually watch and wait until it has grown to a certain size (I believe it's 4cm) before doing surgery.