If an acoustic neuroma comes back, does that mean its a cancer?

Usually not: Recurrence usually means some tumor was left behind and not removed from the first surgery. This can occur if a lot was left behind (macroscopic residual, recurrence more frequent), or even a tiny amount was left behind (microscopic residual, recurrence less frequent). Malignant acoustics are extremely rare and most often occur after prior radiation treatment for a benign acoustic neuroma.

Not usually: Acoustic neuroma may come back if incompletely removed or may grow following radiation, possibly requiring surgery to remove residual tumor.