Final answer:
A mastectomy is performed when a tumor is too large or too serious for a lumpectomy. Surgery aims to treat isolated, solid cancers, and a biopsy is used for diagnosis before surgical procedures.
Step-by-step explanation:
When a tumor is too large or too serious for a lumpectomy, a mastectomy is performed. Surgery is a common intervention for treating isolated, solid cancers where surgeons aim to remove the whole mass along with local lymph nodes if necessary. A biopsy may be conducted prior to surgery to analyze tissue specimens in a medical laboratory for cancer diagnosis. In situations where tumors cannot be removed without damaging vital structures, as it sometimes happens in the brain, other types of treatments are mandatory.