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1.The history given by you suggest presence of cystic structure in the breast.
2.Infective cause (
abscess) excluded due to absence of pain or tenderness.
3.So the possible cause could be
breast cyst, Ductal ectasia ( dilated ducts) and finally mass could not be excluded.
4.You need to see your GP, let it get examined and ask for an
ultrasound breast to characterise the lesion.
5.Ultrsound will help to evaluate the nature of the lesion ( solid, cystic,ductal), its source and where it is extending.
6.Depending on findings further steps like - FNAC in mass lesion ( fine needle aspiration cytology), Fat, ductal cyst lesion followup necessary. Good luck.
Hope it helps you. Wish you a good health.
Anything to ask ? do not hesitate. Thank you.