The picture here shows such a slide. There are very many normal breast cells on the slide, but the diagnosis of cancer is made because of the 10 malignant cells in the middle of the picture. Some hospitals may not have this expertise and will send your microscope slides to another hospital to be examined by this expert. It is performed in the doctor's office and does not require a trip to the hospital or operating room. Pain medications are essentially never required.
Complications are very rare.
The biggest problem is that sometimes the cells removed are not of high enough quality to make a determination if they are cancerous or not. This means that the needle aspiration may need to be repeated, or a more formal open breast biopsy may need to be performed. This technique is performed under local anesthesia and removes a larger core of tissue for examination under the microscope. It still undergoes microscopic examination, but the pathologist handles and stains it differently. Complications continue to be quite rare.