Fine needle aspiration is a useful technique for assessing breast mass cytology in the outpatient setting. Aspiration can be carried out by a clinician but cytological interpretation requires an experienced pathologist.
The non-dominant hand is used to fix the mass within the breast tissue. With the other hand, a 21 gauge needle on a 10 ml or 20 ml syringe is guided through the mass. Then, suction is applied moving backwards and forwards with the syringe for a couple of passes in the same plane. Before withdrawing the syringe, suction is relieved.
The act of applying suction and guiding the needle can be improved with a dedicated 'syringe driver'. The suction should be applied gently. The theory is that suction is only for the purpose of drawing cells into the path of the needle. Hence, the cutting action of the needle tip frees cells and not the shearing effect of suction which would distort cellular morphology.
Once removed from the mass, the contents of the hub of the needle should be rapidly blown with the syringe onto a microscope slide and smeared. Fixative may be with alcohol or air drying. Then, the slides are ready for staining.
On occasion, particularly for impalpable lesions guidance may be required through X ray or ultrasound.
FNAC has a false-positive rate of 1-3% and a false-negative rate of 10-18%. Where the diagnosis remains in doubt e.g. in situ from invasive carcinoma, core biopsy may be required.