Prior to surgery, after my guided needle biopsy (that was positive for cancer) I had MRI and PET scan. Both showed 1 suspicious node. Surgery revealed 7 out of 12 positive. I prepared for possible lymphedema, which started about 2 weeks after radiation finished. Cancer doesn’t follow rules. My care team helped me choose best options post op.

You did not mention which part of your arm is affected, but if it is your hands I highly recommend compression gloves. I had 14 lymph glands removed, and until very recently had no problem with edema. My hands now do swell occasionally and I put compression gloves with the fingers out. They work like a miracle. If I put them on before bed, by morning the swelling is gone. If I wear them during the day the open fingers make it possible for me to do just about everything. They are very inexpensive $15.00. I think I posted a site where you can buy them online. Hope this helps
Gina 5009