Yes likely from lymphadema, very normal, they've removed nodes that usually carry lymph fluid. So it's trapped because the pathways no longer exist. Normally I would suggest lymphatic massage but in your case that's a no. Not with failed margins and further treatment pending. I would wait until after treatment is finished you've and gotten a clear scan before attempting any kind of massage. (This gets the fluid moving and if there's cancer present that's a bad scenario) just know that its normal. Now if the area becomes Hot and red, then I would be concerned about infection. Hugs and best of luck. I would ask just to be on the safe side, the next time you see one of the specialists.