When a dominant breast mass is identified, the presence of a carcinoma must be considered, and biopsy should be performed to establish a tissue diagnosis. About 30% to 40% of lesions clinically believed to be malignant will be benign on histologic examination (20). Conversely, 25% of clinically benign-appearing lesions will be malignant when biopsied (21).
Biopsy Techniques It is preferable for the patient to be involved in planning her therapy. In most instances, initial biopsy can be followed by definitive treatment at a later date. This approach allows the physician to discuss alternative forms of surgical therapy with the patient who has a malignancy. It gives the patient an opportunity to obtain a second opinion before undergoing definitive treatment.
Fine-needle aspiration cytology (FNAC) is usually performed on palpable lesions or under ultrasound guidance using a 20-or 22-gauge needle. The technique has a high level of diagnostic accuracy, with low false-negative rates and rare, but persistent, false-positive results (20,22). In most reported series, false-negative rates range from 10% to 15%, and false-positive rates are generally less than 1%, whereas insufficient specimens account for about 15% of samples (23). If a mass appears malignant on physical examination, mammography, or both, FNAC cytology results can be used for definitive diagnosis, although in these circumstances a core biopsy is usually the biopsy of choice. Negative FNAC results do not exclude malignancy and should be evaluated by either a core needle or traditional excisional biopsy for suspicious lesions. In younger women, it is prudent to monitor a benign-appearing mass for one or two menstrual cycles. Confirmation of a clinically apparent fibroadenoma with FNAC can serve as the basis for observational follow-up without excision. FNAC may be used in cystic lesions to aspirate ﬂuid, especially in benign-appearing cystic lesions. For benign cysts, cytologic examination is not necessary if the ﬂuid is nonbloody and the cyst resolves after aspiration.
Core Needle Biopsy Core needle biopsy (CNB) can be performed on both palpable and nonpalpable breast masses. Performing a core biopsy instead of FNAC on a palpable lesion has the advantage of obtaining more tissue for diagnostic purposes, including tests for estrogen and progesterone receptors and Her-2/neu, and has generally replaced FNAC unless aspiration of a cystic mass is being performed. Core biopsy of nonpalpable breast lesions usually is performed using mammographic or ultrasonographic guidance. MRI-detected lesions that cannot be seen with mammography or ultrasonography may be biopsied under MRI guidance. Mammographic units with computerized stereotactic modifications can be used to localize abnormalities and perform CNB without surgery. Under imaging guidance, a biopsy needle is inserted into the lesion and a core of tissue is removed for histologic examination. Devices with suction assistance often are used to increase the volume of tissue removed for evaluation. A titanium clip often is used to mark the biopsy site and serve as a guide should further excision be required. Ultrasonography may be used to perform core biopsy on a nonpalpable lesion. Because it is less invasive and less expensive than open mammographic localization biopsy, CNB is preferred for accessible lesions. If a definitive diagnosis is not established, these procedures must be followed by open biopsy.