First a mri or sonography, namography will find a tumor , tell you thats its not a cyst, not much looking like a cancer. Look like a fibroadenoma.
Dont let them do needle biopsy, its a weaste of time and not effective in most cases.
A excision biopsy with margin is the fastest and safest procedure, in any result of the biopsy.
Even if malign, the job is done.
If the margin is not clear, resextion need to be done.
They might try radiation in case of malinity to prevent reocurrence, chemo and radiation are not proved to work in sarcoma.
If malign. Tgey will need to do a ct scan to check the rest of tge body for metastases