I just had an MRI on my breast and they report came back and said a lymph nodes on both breast 4 mm not sure if cancer would you do a biopsy?

Lymph. nodes can normally occur within the breasts. If there are no suspicious features, they are benign and require no further follow up.
Nodes, MRI & CA. MRI is very sensitive, but not as specific. This means it shows a lot of things other test can't detect. Does that mean the things are real...yes, but are they normal..most likely. With no other findings on MRI and considering they are on both sides, R and L, I suspect they are part of your normal anatomy. Nodes will often show up on even mammograms but it doesn't mean there is anything in them.