Fine needle aspiration (FNA)

FNA is widely used to evaluate palpable lesions or those detected by mammography. FNA and core biopsies can provide early detection of malignancies without performing open surgical biopsies.
FNA is performed using a 23-25 gauge needle with a 10 mL syringe. A local anaesthetic is usually not used because the resulting swelling may obscure the nodule. A ‘gun’ or ‘pistol’ is often used to stabilize the syringe/needle set-up. Because many breast lesions are densely fibrous, a larger (22 G) needle can be used, and in this case local anaesthesia may be advisable.
The centre, and not the periphery, of a mass should be aspirated. After placing the needle in the center of the lesion, suction is applied via the syringe. Suction should be released when blood or other material is first seen in the hub of the needle, which is withdrawn from the lesion having released the  vacuum suction, in order to avoid the cells being sucked into the syringe (rather than staying in the needle). In case some fluid is obtained from a cyst, negative pressure should be maintained until the cyst is completely drained, and if there is a residual palpable mass, it should be re-aspirated.
The needle is then removed from the syringe, the syringe filled with air and after refitting the needle , the  the plunger of the syringe is pressed, a small drop of aspirated material is expressed onto each slide and smears are prepared. The needle should be washed with a preservative solution for cell block or liquid-based cytology preparations, in order to harvest as much of the sample as possible. The accuracy of liquid-based preparations is comparable to that obtained with direct smears, although the cytological appearance is slightly different.
Complications of FNA are rare. The most common is bleeding. Occasionally, FNA can cause infarction of the lesion, particularly in fibroadenomas.
The accuracy of FNA is highly operator dependent. Sensitivity for malignancy is high. False positive results are uncommon, whereas false negative results may occur because of errors of sampling or interpretation. Satisfactory specimens are usually more likely when FNA is performed by a cytopathologist.
FNA has some limitations. Although sensitive in detecting ductal carcinomas, it cannot distinguish an invasive ductal carcinoma from a ductal carcinoma in situ. It cannot identify lymphatic or vascular invasion. The diagnosis of some malignant tumours, such as lobular carcinoma and tubular carcinoma, requires considerable experience. Aspiration of a breast cyst is certainly therapeutic, but whether cyst fluid needs cytological examination is controversial. The great majority of them are benign; however, a small number of carcinomas are cystic.

Evaluation of FNA specimens

Low power evaluation

• Cellularity
• Cell arrangements
• Background elements

Cellularity is important, although there is considerable overlap between categories. Hypocellular aspirates are commonly obtained from fibroadenoma, fibrocystic changes, fat necrosis, radiation changes and carcinoma (particularly scirrhous, tubular and lobular types). Moderately cellular aspirates are seen with fibroadenoma, phyllodes tumours, fibrocystic changes and carcinoma. Hypercellular aspirates are common in some fibroadenomas, phyllodes tumours and invasive carcinoma.
Cells can be arranges in sheets (such as in fibroadenoma, fibrocystic changes, or lobular carcinoma in situ), tightly cohesive three-dimensional clusters (fibroadenoma, phyllodes tumour, intraductal papilloma and hyperplasia, lobular and ductal carcinoma in situ, mucinous carcinoma), loosely cohesive clusters (phyllodes tumour, ductal carcinoma in situ), branching papillary clusters (fibroadenoma, intraductal papilloma, papillary carcinoma). Numerous isolated cells are characteristic of breast carcinoma. Regular nuclear spacing in clusters suggests a benign lesion, whereas irregular spacing is characteristic of malignancy.
Background elements include inflammatory cells, amorphous debris, fresh and old blood, and mucin. Acute inflammatory cells are seen with mastitis and necrotic carcinomas, whereas chronic inflammatory cells can be seen with intramammary lymph nodes and medullary carcinoma. An amorphous granular debris suggests malignancy, but it can also be found in benign conditions, such as apocrine metaplasia. Blood suggests an intraductal papilloma or a carcinoma. Mucin is observed with fibroadenoma or mucinous carcinoma.

High power evaluation

• Types of single cells
• Nuclear features
• Cytoplasmic features

Isolated cells are epithelial or mesenchimal in origin; they may be intact or stripped of cytoplasm (naked nuclei). Single epithelial cells are seen with carcinoma, whereas mesenchymal cells suggest fibroadenoma, phyllodes tumour or sarcoma, but they can also be present in invasive carcinoma. Naked nuclei are common in fibroadenoma. Inflammatory cells, including histiocytes, are common in fat necrosis, mastitis and fibrocystic changes.
Nuclear atypia (nuclear enlargement and pleomorphism, large nucleoli) is observed in moderately and poorly differentiated ductal carcinomas. However, some malignant tumours, such as tubular, lobular and mucinous carcinoma, show very little nuclear atypia, and the recognition of other features (architecture, abundant extracellular mucin) is important in the diagnosis of these tumours.
Some cytological features are characteristic of some breast lesions. Apocrine change is seen in apocrine metaplasia and apocrine carcinoma. A vacuolated cytoplasm is observed with some carcinomas, including mucinous and lobular carcinoma.