Cytopathology is a specialized branch of pathology related to the study of cells derived from either fine-needle aspiration biopsy (FNAB) or exfoliation including effusions, washings, brushings, or body fluids. FNAB is performed using a 23- or 25-gauge hypodermic needle attached to a 10-mL plastic syringe. FNAB can be performed blindly for palpable masses or under radiologic guidance including ultrasound (US), computed tomography (CT), or magnetic resonance imaging (MRI) for nonpalpable lesions. Specimens obtained from any of these sources can be prepared in several ways for conventional cytopathologic evaluation and ancillary studies. Smears can be made directly or from the cell pellet obtained after centrifugation of the specimen following admixture with a liquid base such as RPMI or Cytolyt solution. Monolayer preparation of the specimen can also be made using different techniques such as Thin Prep and Sure Path. Smears prepared by any of the techniques are usually fixed in alcohol for Papanicalaou staining, or air-dried for Diff-Quik staining. In addition, aspirated material from FNA or exfoliative specimens can be rinsed in RPMI or Cytolyt solution to prepare tissue blocks that are fixed in formalin, processed routinely similar to surgical tissues, embedded in paraffin, and subsequently cut at 5 μm and finally stained by the hematoxylin and eosin (H&E) method.
The popularity of core needle biopsy (CNB) has to a large extent reduced the performance of FNAB in many centers. CNB produces cores of breast tissue that are generated by introduction of automated spring-loaded devices that activate a 14- to 18-gauge cutting needle into the localized site. Unlike FNAB, CNB not only provides tissue architecture that facilitates interpretation but also adequate tissue for performing ancillary studies. In contrast to CNB, FNAB is however better tolerated, less invasive, and allows more effective sampling of small-sized lesions. Moreover, the possibility of sampling multiple sites in a large-sized lesion is an added advantage. FNAB is also the preferred technique for investigating breast lesions close to the chest wall because of fear of causing pneumothorax with a CNB or for investigating lesions occurring in breast with any type of tissue expander because of the risk of puncturing the latter. FNAB, however, may yield very minimal material insufficient for diagnosis particularly in sclerotic lesions necessitating the performance of CNB. For primary breast masses, the inability of FNAB to distinguish in situ from invasive carcinomas is a major disadvantage, which has essentially led CNB to replace FNAB for initial investigation of index breast lesions that are deemed to be very suspicious for malignancy on clinical examination and imaging findings. It should be noted, however, that FNAB and CNB are complementary techniques and can be used alone interchangeably or in conjunction based on the requirement of individual cases for preoperative diagnosis. The golden rule for the interpretation of breast FNAB is to always correlate the cytologic findings with clinical and imaging findings, commonly referred to as the triple test. Any discrepancy between the 3 components of the triple test should lead to ...