Thank you for the query.
What you are talking about is most likely lipoma
- a very common benign tumor
of the soft tissues. It can have vary sizes and there is no size which would be life threatening. This tumors does not get cancerous. The only reason it can be removed is cosmetic reason.
If you want to take a precaution, and dont want to remove it, ultrasound
should tell what kind of tissue is inside this lump.
Hope this will help.