what type of growth could my hamster be dealing with ?

hi, i am concerned about my robo dwarf hamster. she is maybe 1 year old ? im not sure i, have had her for about 5 months now. and i have noticed that she is forming a growth around the left side of her neck and into her ribs. she seems to be healthy and happy. and she does not seem to be in any type of pain. she has been running around and eating. should i take her to veterinarian ? or should i wait a couple of days/ months and see how she progresses ? i need help. can u tell me maybe what im dealing with, with my hamster ? your help would be appreciated.

thank you, littlechica.