Is it possible for lymphodema to occur four years after having a lumpectomy?

Yes: Unfortunately not that rare if you had a node dissection or nodal radiation. Check with your surgeon - there are treatments available that may help.

Yes,: However it would be unusual unless axillary lymph nodes were removed at the same time. Once nodes are damaged (radiation therapy) or surgically removed, one is set up for lymphedema in that arm. It can suddenly manifest even years later after trauma or infection to that hand or arm occurs.