I want to get some more detail information about your problem-
What is the size and shape of the mass?
Is it soft or firm or fluid containing sac?
Is it movable or fixed?
Do you have any other disease?
Do you take any other medicine?
Waiting for your reply.
Thank you for the information.
The swelling under your arm is possibly due to lipoma or the benign tumor of the fatty tissue which is harmless.
The other possibility may be a cyst.
Physical examination by a doctor will be needed to confirm the diagnosis.
I would advise you to contact your physician or a surgeon for evaluation.
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