Biopsy of a suspicious breast mass may be accomplished by needle sampling or by open excisional biopsy. When needle sampling is done, a "fine" aspiration biopsy will confirm the presence of malignant cells while a "core" can diagnose invasion and provide tissue for further processing. As to open biopsy, if ever excision is contemplated within the context of a possible cancer, marking of margins or the inclusion of a rim of normal tissue around the mass must be done where feasible (in effect, a lumpectomy). This is to minimize the need for further radical surgery.
If the breast mass biopsy is positive, staging is done & treatments are planned accordingly. (How I hate it when stage IV patients have wasted time & money on pointless radical surgery before they get the treatment they really need!) The staging tests ordered would depend on a thorough history & physical examination, but chest x-rays, mammography, a bone scan, liver ultrasound, or CT scans may be requested. Special stains are sometimes done on the biopsy specimen at this point for hormone receptor assays & her2/neu (cerbB2) growth factor receptor, especially if preoperative treatments are contemplated.
In non-metastatic invasive breast cancer of the non-inflammatory type, an operation is always a component of cure. For stages I & II, Breast Conserving Surgery is ideal in the absence of any compelling contraindication. BCS, aka "lumpectomy" or "partial mastectomy", involves a wide excision of tumor with a cuff of normal tissue around it. It entails subsequent radiotherapy but affords the same control rates as a standard modified radical mastectomy with better cosmetic results. A better feel & shape than an implant in most cases anyway. (By the way, while there are additional technical considerations, BCS is not prohibited for tumors near the nipple or where implants are in place.) Axillary lymph node sampling is also done with BCS, through a separate armpit incision. This sample extent depends upon whether you've presented with apparent node involvement or not. If none are clinically evident, just a biopsy of the "sentinel node" may be done. Axillary node status is just prognostic and not all nodes need to be removed. The extent of their involvement gives your docs added staging information to guide postoperative treatments.
What should make you think twice about lumpectomy? When is a modified radical mastectomy the better option? Well, BCS requires re-excision should the margins of the lumpectomy specimen remain positive. Radiotherapy is a necessary component, so those who can't take that treatment are best served by breast removal (eg. early pregnancy). BCS is also suboptimal if tumors are multiple. The same is true if the mass is large relative to the breast's size, although preoperative (neoadjuvant) chemotherapy may be considered to enable BCS in such cases.
Where all things are equal and no contraindications to BCS exist, the important factor is the fully informed patient's preference.
As for surgeons… I know of a busy one who said that breast cancer operations are glorified excisions to sleepwalk through. For a minute there, I'd thought that I was talking with God (or a neurosurgeon) but… no; This doc still comes alive for each hair-raising Whipple's procedure. Would that all constructive thrill-seekers have that level of experience & expertise, not to mention stamina. In reality, what may be almost reflexive & forthright for some is an uncommonly complex job for others. Find yourself an oncology team with a great surgeon!