[2] The most appropriate method of biopsy for a patient depends upon a variety of factors, including the size, location, appearance and characteristics of the abnormality.

[7] Typical indications include: Fine-needle aspiration (FNA) is a percutaneous ("through the skin") procedure that uses a fine needle and a syringe to sample fluid from a breast cyst or remove clusters of cells from a solid mass.

[12] However, in up to 30% of cases, pathological slides from fine-needle aspiration of breast lesions may be inconclusive, necessitating the need for further testing.

[11] A spring-loaded sheath then is triggered by the technician that covers the trough in the needle to allow sample tissue to be separated and removed for analysis.

To prevent the need to pierce the breast repeatedly, a coaxial needle is left in place on top of the mass as a guide.

[11] CNB has a higher sensitivity for cancer than FNA, has lower false negatives, and has proven more successful in finding rare breast diseases like lobular carcinoma.

[14][11] Also, because breast tissue can be difficult to target on ultrasound, as many as 5–10% of suspicious lesions are missed by the needle and may result in a high rate of false negatives, or the need for additional biopsies.

This method has become more popular than FNA, CNB, and surgical biopsies due to the benefits of low invasiveness while still obtaining a larger tissue sample.

[17][18][19] Excisional biopsy involves surgically removing the suspicious area of the breast to examine it under the microscope for diagnosis.

[14] Some examples of adverse effects of core needle biopsies can include rare biopsy risks like infection, abscess formation, fistula formation, migration of any markers placed in the breast, and potential seeding of the tumor (causing displacement of cancer cells due to the procedure that can start new tumors elsewhere).

[21] Bleeding into the site of the suspicious lesion caused by the biopsy procedure can appear to look like a complex cyst on ultrasound, which could lead to additional unnecessary management.