Core Biopsy

So my problem is, I am a breast cancer survivor,for 3 years. as you guys know once youve had cancer life is just never the same. I had a CT scan that showed a retroperitinium mass. MRI confirmed. suspicious of sarcoma. I have this horribe insurance BAY CARE CIGNA through my employer. My oncologist is againt a biopsy as he stated that if its sarcoma the cells can metastacise to the neddle. referred me to Moffett ccancer. the specialist there states he is comfortable doing a core biopsy as they use a protected sheath. INS refuses to pay. Wants me to go to there hospital. My question is has any one had this kind of biopsy CORE. and was it done by a radiologist vs a specialist