"In a word, swelling. Extra fluid builds up in your tissue when your lymphatic system isn't working well, usually because your lymph nodes were damaged or removed."
https://www.webmd.com/breast-cancer/ss/slideshow-lymphedema?ecd=wnl_spr_101426&ctr=wnl-spr-101426_supportTop_title_1&mb=Bw69jj4V%403Xd0vWN4nAvZhsBxqZqfebCTdGTM0BbxsM%3d