Welcome to Health care magic. 1.The history suggest that it could be a lipoma ( fat cell content mass lesion) because long standing and pain less, no significant growth. 2.Next possible cause could be cystic structure, also seen pain less and may remain for longer time, finally lymph nodal pathology can not be ruled out. 3.In this case i would recommend a ultrasound scan to evaluate the sours of lesion / lump and its nature ( cystic, solid, vascular) and where all its extending can be assessed. 4.There is a risk probably - so your treating doctor has kept you on the aspirin on daily basis. 5.So when you visit doctor next time try to get the scan done. An FNAC - will help to know the cells of the lesion ( fine needle aspiration cytology) Good luck. Hope it helps you. Wish you a good health. Anything to ask ? do not hesitate. Thank you.