PS: if the lump is indeed benign, then 'no', there is no danger of it turning malignant.
If the lump you have is pretty small, then a FNAC is probably adequate and your lesion is a benign cyst or adenoma. Those lumps are very common.
On the other hand, if the lump is very large then a FNAC could have missed something that in other parts of the lump that the needle didn't penetrate.
I would probably trust my doctor and his/her judgement about your lump.
Maybe someone else here has a different view. Katrin