Stereotactic Breast Biopsy

Mark P. Bowes, PhD


*Medical Writer, Portland, Oregon.
Address correspondence to: Mark P. Bowes, PhD, Medical Writer, 7135 SE 18th Avenue, Portland, OR 97202. E-mail: mpbowes@gmail.com.

Disclosure Statement: Dr Bowes reports having no financial or advisory relationships with corporate organizations related to this activity.

ABSTRACT

Although the use of mammography for breast cancer screening reduces the risk of breast cancer mortality, most abnormalities that are identified on screening mammograms are not breast cancer. Breast biopsy is essential for cancer diagnosis and treatment selection, and is indicated for approximately 2% of women who undergo screening mammography. Surgical biopsy entails removal of the suspect lesion identified on mammography, and for many years was the only option for obtaining adequate tissue specimens for histologic analysis. Over the last 2 decades, several percutaneous biopsy options have become available. Percutaneous biopsy provides a less invasive alternative to surgical biopsy, with a high rate of accuracy and good safety and patient acceptability. Stereotactic biopsy uses a pair of digital or analog mammography images obtained from 30 degrees apart to calculate the depth of a target lesion below the surface. The stereotactic method may be used with a variety of biopsy devices and needle sizes to quickly obtain tissue samples for histologic assessment. Successful stereotactic biopsy technique requires the consideration of several factors, including the patient's previous mammography findings, the location of the target lesion within the breast, correct positioning of scout images and images obtained before and after deployment of the biopsy device, and ensuring that there is a sufficient margin of tissue between the tip of the biopsy device and the back of the breast. Failure to correctly position and deploy the biopsy device may result in underestimating the extent of the patient's disease, or it may necessitate additional imaging sessions or surgical biopsy. Stereotactic biopsy is generally safe and well tolerated by patients, with a low incidence of serious adverse outcomes.

Introduction
Breast cancer is the most common cancer of women in the United States, excluding cancers of the skin, and the second leading cause of cancer-related mortality.1 More than 280 000 new cases are diagnosed each year, more than 39 000 women die of breast cancer, and approximately 2.6 million women in the United States have a history of previous breast cancer. The lifetime risk that a woman will develop invasive breast cancer is approximately 1 in 8, and the lifetime risk of dying from breast cancer is 1 in 35. Although more common in women than men, approximately 2100 cases of breast cancer are diagnosed in men each year, and approximately 450 men are expected to die of the disease in 2011.1

Several clinical studies have shown that screening women using mammography significantly reduces the risk of breast cancer mortality.2 The beneficial effects of screening are greater in older women, and become more notable when patients are followed-up over longer periods of time. A recent analysis of outcomes over a period of nearly 30 years found that screening mammography reduces a woman's risk of breast cancer mortality by approximately 30%.3 The American Cancer Society recommends that women over the age of 40 should undergo annual mammography for as long as they remain free of serious health problems. Women with certain high-risk features should undergo screening with magnetic resonance imaging (MRI) in addition to a regular mammogram.4 Although mammography is important for the early recognition of disease, fewer than 1% of patients with a suspicious mammogram actually have cancer. Therefore, most abnormal mammograms are false-positive findings that require additional evaluation.2 The objective of a breast biopsy is to obtain cells for microscopic evaluation from a suspicious breast lesion. Although very small lesions may be completely removed in some cases as a result of the biopsy procedure, the removal of suspected cancer is not the objective of the biopsy. Examination of biopsy samples by a pathologist is often essential in diagnosing suspicious breast masses, determining how far the patient's cancer has advanced, and deciding on a course of treatment.

Since its initial introduction in the 1990s, stereotactic breast biopsy has increasingly been used as an alternative to surgical biopsy of suspicious breast masses.4 The stereotactic biopsy procedure is usually fast, relatively pain free, and similar in accuracy to more invasive surgical biopsy. Positioning difficulties and procedural errors during the biopsy process may cause treatment delays and require patients to undergo additional procedures. This article will review the indications for breast biopsy, the selection of appropriate patients for stereotactic biopsy, the advantages and limitations of the stereotactic biopsy approach, and important patient considerations for successfully performing stereotactic procedures.

Breast Cancer
Cancer is a disease that is characterized by abnormal cell growth and development. In solid tissues such as the breast, cancer is usually seen as a tissue mass (or tumor), and it may also spread (metastasize) to other tissues. Cancer cells may be carried in the lymphatic system, a network of vessels that are similar to veins that drain fluid, waste, and immune cells from the tissues to the lymph nodes. Cancerous cells may also spread beyond the lymph nodes to more distant tissue sites throughout the body. Cancer of the breast generally originates in either the lobules, the spherical glandular structures that are the site of milk production, or the mammary ducts, which connect the lobules to the skin surface at the nipple.1 Uncontrolled tumor growth and spread of cancer throughout the body are often life threatening.

Breast cancers may be either invasive or noninvasive.6 Invasive, or infiltrating, cancers originate in the lobules or ducts but break through the lobule or duct wall to invade the surrounding tissues. Invasive (or infiltrating) ductal carcinoma, an invasive cancer that originates in the milk ducts, is the most common type of invasive breast cancer, accounting for approximately 80% of cases. Invasive (or infiltrating) lobular carcinomas, which are invasive carcinomas that originate in the lobules, account for approximately 10% of invasive breast cancers. Other, less common types of invasive disease together make up approximately 10% of invasive breast cancers. These include the following6:

Noninvasive breast cancers, which are also called in situ cancers, are confined within the ducts or the lobules. Noninvasive cancers of the ducts, or ductal carcinoma in situ (DCIS), account for approximately 83% of noninvasive cancers of the breast among women, whereas noninvasive cancers of the lobules, or lobular carcinoma in situ (LCIS), account for approximately 11% of female in situ breast cancers. Other in situ cancers may have features of both DCIS and LCIS, or may be of indeterminate origin.1 Many oncologists do not consider LCIS to be a form of cancer, but rather a marker of increased future cancer risk, although the classification and appropriate management of LCIS is currently a controversial issue in oncology.7

Finally, not all breast masses or suspicious imaging findings are breast cancer. In fact, most suspicious breast masses are benign, do not grow uncontrollably, and are not life threatening.1 Benign breast lumps may include fibrotic tissue or cysts, fibroadenomas (smooth, solid lumps of glandular and fibrous tissue), and intraductal papillomas (small, noncancerous, wart-like growths that form within the milk ducts).8 In addition, some noncancerous diagnoses are considered important because they are associated with an increased risk of future cancer. For example, atypical ductal hyperplasia and atypical lobular hyperplasia are conditions in which there is excessive growth of cells of the mammary ducts or lobules, with some cells exhibiting an abnormal appearance on microscopy. Although not cancerous, these conditions are associated with an increased risk of future breast cancer.9

As with most other types of cancer, breast cancer is more easily treatable when it is identified early, before it has had the chance to spread to other tissues. Breast cancer may be defined as localized (confined entirely to the breast), regional (involving the lymph nodes), or distant (metastasized beyond the lymph nodes). Overall, 89% of patients diagnosed with breast cancer are alive 5 years after the diagnosis, and 77% are alive after 15 years. However, the 5-year survival rate is approximately 99% for patients diagnosed with local breast cancer, 84% for those with regional disease, but only 23% for patients with distant metastases.10 These survival statistics demonstrate that breast cancer screening and early diagnosis are essential to reduce the risk of mortality.

Indications for Breast Biopsy
Approximately 1.5 million breast biopsies are performed each year in the United States.11 Depending on the results of the initial mammogram, further evaluation may be needed to assess whether a suspicious finding represents breast cancer, another type of pathology, or normal tissue. Roughly 10% of women who undergo a screening mammogram will require some type of follow-up evaluation, with approximately 2% requiring some type of breast biopsy.2 Of breast lesions that are biopsied, approximately 80% of lesions are benign and 20% are cancerous.13

A positive finding on a screening mammogram may be followed with a diagnostic mammogram, which is a radiographic examination to evaluate patients who have signs or symptoms of breast disease, imaging findings of concern, or previous imaging results that require specific follow-up. Diagnostic mammography may include additional views to evaluate an area of clinical or radiographic concern.14 Breast biopsy may be indicated following mammography or other imaging results. The American College of Radiology (ACR) uses the Breast Imaging Reporting and Data System (BI-RADS) to classify the results of breast imaging using standardized terminology and methods for mammography, MRI, and sonography.15 Mammogram findings are classified into 7 levels, each of which is accompanied by a recommended follow-up evaluation (Table). Patients who have undergone screening mammography with BI-RADS scores of 4 (Suspicious Abnormality) usually require a biopsy; optional subdivisions are used to provide additional information about the patient's specific situation. Those with BI-RADS scores of 5 (Highly Suggestive of Malignancy) require biopsy or surgical evaluation and treatment. Some patients may undergo biopsy with lower BI-RADS scores. For example, a biopsy might be performed for a patient with a BI-RADS score of 3 who is very anxious about the possibility of breast cancer.12

The ACR also notes that a negative mammogram does not absolutely rule out cancer, and there will always be some individuals who have breast cancer despite negative mammography findings. Clinically suspicious lesions should be biopsied even if mammography is negative.15 Finally, it should also be noted that the same BI-RADS codes are used to record the results of breast cancer evaluations in male patients.15

Types of Biopsy: Overview
In general, breast biopsies may be classified as either surgical biopsy or percutaneous (needle) biopsy.

Surgical biopsy is the removal of the suspicious mass as well as surrounding healthy tissue. Patients may require hospitalization and general anesthesia. As with any surgical procedure, biopsy may be associated with a prolonged recovery time and greater overall cost.16 When first used for patients with possible breast cancer, surgical biopsy was limited to individuals with palpable breast lesions. The introduction of mammography and other imaging techniques made it possible to biopsy lesions that are not detectable by palpation.12

Percutaneous biopsy (also referred to as needle biopsy) provides a minimally invasive alternative to surgical biopsy, with fewer procedural complications, better cosmetic results, less scarring that might interfere with future breast imaging, without the need for hospitalization or general anesthesia, and with lower overall cost.12,17 Fine-needle aspiration biopsy (FNAB) was the first percutaneous alternative to surgical biopsy.12 FNAB uses cytology (the examination of isolated cells) to diagnose cancer, and it is also referred to as fine-needle aspiration cytology. Only a small amount of fluid and tissue is extracted from the lesion. In general, clear fluid is more likely to indicate a benign finding; bloody or cloudy fluid may indicate either a benign or cancerous finding.16 Guidelines from the National Cancer Institute recommend that FNAB should be performed using a 22-guage to 25-guage needle, using 2 to 4 passes, each of which involves up to 15 up and down motions. FNAB is used less often for breast cancer biopsy in the United States than in other countries because there are relatively few trained cytopathologists in the United States and because histology (which examines the overall structure of the tissue sample) is generally preferred to cytology for diagnosing breast cancer.12 FNAB is also limited by a relatively high rate of insufficient tissue sampling and a high false-negative rate in some studies.11 In the United States, FNAB is usually performed using sonography guidance. A second percutaneous technique is core-needle biopsy, which has become more commonly used in the United States. Image-guided core-needle biopsy uses larger needles to withdraw a cylinder (core) of tissue from a suspected breast lesion.16 The needle is usually inserted 3 to 6 times, and the samples are evaluated histologically by a pathologist. Core-needle biopsy yields a larger volume of tissue than FNAB, and is generally more accurate for the diagnosis of breast cancer. FNAB and core-needle biopsy are illustrated in Figure 1.13,18 More recently, the use of vacuum-assisted large-needle biopsy has become more common. A hollow probe is inserted into the lesion, tissue is withdrawn by suction, and sections are cut from the surrounding breast with a rotating knife or by radiofrequency energy. Vacuum biopsy devices yield even more tissue than core-needle biopsy devices, and with sample sites that are evenly spaced around the insertion point.

With the continued refinement of imaging and sampling techniques over the last several decades, image-guided percutaneous biopsy has become the most commonly used procedure for the follow-up evaluation of breast lesions detected on mammography.17 A variety of imaging techniques are available for use with percutaneous biopsy, including stereotactic guidance, sonography, and MRI. These techniques have changed the way that patients are evaluated for possible breast cancer, and have significantly reduced the number of patients who require surgical biopsy. Stereotactic guidance allows precise needle sampling of a suspicious breast lesion that was identified on a mammogram.17 Stereotactic X-ray imaging may also be used to place a guidewire within the suspected tumor to make it easier to locate the lesion during a surgical biopsy. Most studies have reported that the false-negative rate with stereotactic biopsy (ie, the number of patients who have a normal finding on biopsy but who actually have cancer when diagnosed surgically) is approximately 1% to 5%.19

Sonography guidance is preferred in some cases because it is simpler, more comfortable for the patient, does not involve ionizing radiation, and may be faster. However, sonography is less effective for targeting certain types of lesions, including small masses, lesions with breast tissue distortion, and lesions with microcalcifications, or small calcium deposits clustered together within the breast tissue.12,20 MRI guidance is often useful for lesions that are not well visualized with mammography. The variety of imaging modes makes it possible to view lesions with a high degree of anatomic detail, including those that are not easily viewable on a mammogram.21 Factors that influence the type of biopsy used include ability to visualize lesion, lesion type and location, position within breast, as well as the availability of specific imaging instruments and the practitioner's experience.17

Stereotactic Breast Biopsy
Stereotactic biopsy is the use of paired digital or analog mammography images obtained from different angles to precisely determine the location of a biopsy target in 3 dimensions. Current methods make it possible to position the biopsy device to within approximately 1 mm of the target.16 The field of view of the different stereotactic systems varies among manufacturers, but is approximately 5 x 5 cm. Stereotactic biopsy is usually used to guide the placement of a biopsy needle for patients with nonpalpable masses or microcalcifications that are not easily identifiable with sonography.12

Indications and Contraindications for Stereotactic Breast Biopsy
According to guidelines from the ACR, stereotactic biopsy is indicated after mammography for the primary diagnosis of the following17:

In addition, criteria published by the Radiological Society of North America include22:

Needle biopsy may be especially challenging in some patients due to individual medical or other factors. Deciding to perform a biopsy requires consideration of the patient's unique clinical circumstances, and there are few criteria that definitively rule out stereotactic biopsy for all patients. Some factors that may direct the treating physician to another type of biopsy include16:

Stereotactic Biopsy Procedure
Stereotactic breast biopsy uses the method of parallax to calculate the 3-dimensional location of the target lesion in space from a pair of 2-dimensional images. Parallax is the change in the apparent location of a stationary object that occurs when the object is viewed from different locations. Stereotactic biopsy uses the parallax between 2 mammography images that are offset from one another by 30 degrees to calculate the depth of the lesion below the breast surface, in much the same way as the eyes use binocular vision to calculate depth perception.12,23 The location of the lesion in space is typically expressed using rectangular, or Cartesian coordinates, with x, y, and z axes that intersect at right angles to one another representing width, height, and depth.23 Alternatively, the target may be localized using polar coordinates, in which horizontal and vertical orientations are measured from a reference point in angular degrees, and distance is measured in millimeters.12 Regardless of the specific coordinate system used, the lesion must be clearly defined and accurately positioned on both stereo images in order to correctly place the biopsy needle within the breast. Positioning difficulties or the failure to visualize the lesion on both views are most likely to result in calculation errors for the z value (depth).23

The rationale for the stereotactic imaging method, potential sources of imaging error, and ways to overcome these barriers were reviewed in detail by Carr et al.23 The breast is compressed between a compression plate and back breast support in order to ensure that the lesion remains in a fixed point in space. An initial scout image is obtained with the X-ray beam perpendicular to the compression plate. This image is used to center the lesion in the field of view, and 2 additional X-ray images are obtained with the X-ray source positioned at +15 degrees and -15 degrees. The projection of the 3-dimensional location of the lesion onto a pair of 2-dimensional images is shown in Figure 2.23 Obtaining radiographs at an offset of +15 and -15 degrees results in the shifting of the target on the 2 resulting images. A computer program uses this parallax shift to calculate the depth of the lesion (the distance along the z dimension). However, in order to interpret the relationship between the parallax motion and the target depth, it is essential to know whether the center of rotation is placed in front of or behind the target (Figure 3).23

Stereotactic breast biopsy is usually performed using a dedicated prone breast biopsy table with the breast placed through an opening in the underside of the table.24 Stereotactic biopsy may also be performed with a conventional upright mammogram device using an add-on stereotactic unit. Both the prone and upright approaches have benefits and limitations. Add-on devices have generally been less popular than stand-alone prone tables because the ability of patients to more easily view the procedure may be associated with an increased likelihood of vasovagal reactions and syncope.11 The prone table also makes it possible to take advantage of gravity to assist with posterior lesions, as well as greater workspace under the table.11 A disadvantage of the prone biopsy approach is that the table occupies a large amount of space in the imaging facility when not in use. Add-on stereotactic devices have also been successfully used to perform stereotactic biopsy for patients in the lateral decubitus position or in a reclining chair.25,26

After the initial set of images has been obtained and the lesion depth calculated, a small incision of the breast is performed, usually a few millimeters in length. The biopsy needle is placed within the lesion, and stereo images are obtained a second time to confirm placement. Tissue samples are then collected, and postfire images are obtained with the sample collecting needle in its extended position to ensure that the lesion is adequately sampled (Figure 4).27 The biopsy probe is withdrawn and a final image is obtained. If the lesion has been mostly or completely removed by the biopsy procedure, a metal clip is placed at the lesion site so that it can be located if the tissue sample reveals that the lesion is cancerous.20 If the target lesion contains calcifications, a sample radiograph may be performed to verify correct sample acquisition.24,28

Several needle biopsy devices may be used in stereotactic breast biopsy procedures. The 14-gauge core cutting needle was initially the standard biopsy device. This probe uses a spring-loaded mechanism that launches the needle into the breast tissue. An outer sleeve advances and cuts the tissue, resulting in a tissue sample contained within the needle shaft. The needle is then withdrawn and the tissue is collected. A core-needle biopsy device removes 1 sample of breast tissue with each insertion. Some devices have more than 1 sampling notch length, which is important to know when setting the probe depth.12 When possible, the longest sampling notch is generally used in order to capture the maximum amount of tissue.

More recently, directional vacuum-assisted devices have replaced the 14-guage cutting needle device for many biopsy procedures. This device uses vacuum to pull breast tissue into a needle, where it is cut and transferred to a sample storage chamber. The advantage when using this device is that it is not necessary to withdraw the needle after each tissue sample. It also makes it easier to obtain tissue in an orderly pattern by rotating the probe, which ensures that the entire region around the lesion is sampled with only a single device placement.20,24 Vacuum biopsy probes are available in a variety of sizes, including 7, 9, 10, 11, 12, and 14 gauge.12 A recent expert consensus conference on diagnosis and treatment of image-detected breast cancer recommended the use of vacuum-assisted biopsy to reduce sampling error and minimize the risk of underestimating disease.28 Vacuum-assisted stereotactic biopsy has been proven to reduce the need for surgical biopsy in more than 70% of patients with microcalcifications and in 85% of patients with solid lesions, while reducing the overall cost of biopsy by an average of 20% compared with surgical biopsy.29

Procedural Steps and Potential Pitfalls
Successfully performing stereotactic breast biopsy requires identifying and overcoming several potential barriers.11

Evaluate the Mammogram and the Patient to Choose the Approach to the Breast
Certain lesions may be more difficult to image, including low-density nodules or diffuse, faint microcalcifications. Poorly defined asymmetrical lesions may reflect overlapping fibroglandular tissue. Some patients may not be candidates for stereotactic biopsy, including those with neurologic or musculoskeletal conditions that make positioning on the biopsy table more difficult or uncomfortable. Medical conditions that cause the patient to move unpredictably (eg, coughing due to respiratory conditions), or those with anxiety or claustrophobia, may also not be appropriate for the procedure. In some cases, the lesion may be well visualized on the scout image but not on the 2 stereo images, which may reflect the superposition of fibroglandular tissue over the target lesion in one of the stereo images. In these cases, the scout image may be used in place of one of the stereo images, and the target lesion depth is calculated using a 15-degree offset angle rather than a 30-degree offset angle.

Patient Characteristics and Positioning
Patients with lesions against the chest wall or along the axilla may be especially difficult to image. Positioning the patient on a prone biopsy table with her arm through the table opening may make it possible to compress and image posterior or difficult to access lesions. Patients with smaller breasts may be at increased risk of puncture of the chest wall with large-gauge biopsy needles.16

Obtaining Scout and Stereo Images The patient and breast should be positioned so that the lesion to be imaged appears well centered in the scout image. If the lesion does not fall within the middle third of the scout image, the lesion may not appear on one of the stereo images. Problems may also occur when the lesion is positioned either too superficially or too deeply within the breast.11 If the lesion is too shallow, the opening on a vacuum-assisted device may extend beyond the surface of the skin, preventing the formation of a good vacuum and resulting in poor tissue sampling. In addition, newer biopsy instruments that use radiofrequency cutting to collect skin samples may cause skin burns if they are positioned too superficially. In contrast, if the lesion is too deep, firing of the probe device (especially spring-loaded biopsy devices) may result in the probe striking the back of the breast or the rear image receptor. This is referred to as a negative stroke margin: the stroke is the distance that the probe tip travels after firing, and the stroke margin is the distance from the tip of the probe before firing and the back of the breast (Figure 5).30 Negative stroke margin occurs when the stroke margin is less than the stroke. Each biopsy device has its own stroke length. It may be necessary to slowly advance the needle into the lesion by hand rather than firing it with a biopsy device.16

Patient Anesthesia and Skin Preparation
Local anesthesia with epinephrine should be avoided. The constant pressure of the compression paddle restricts blood flow and may cause skin necrosis. Epinephrine may be used with deeper injections into the breast parenchyma.11

Recognizing Specific Insertion Depths for Individual Devices
The biopsy system software places the tip of the probe device at a specific depth within the tissue. However, some devices must be placed at a depth less than that calculated due to differences between biopsy devices in the forward motion of the needle and the amount of dead space at the tip. This pullback must be entered correctly for the individual biopsy device, or the needle tip will not be placed correctly.

Confirming Location of Biopsy Needle Tip Relative to Lesion
Before firing the biopsy device and obtaining a sample, new stereo images are obtained showing the placement of the needle tip within the lesion. The lesion may move when the biopsy tip is inserted, which can alter the depth of the lesion below the breast surface.

Sampling the Lesion
Inadequate tissue sampling may result in an incorrect diagnosis of the breast lesion. For example, lesions diagnosed by needle biopsy as atypical hyperplasia are often upgraded to carcinoma after a surgical biopsy of the lesion. Microcalcifications may require more tissue sampling to ensure that there is adequate tissue for a diagnosis. A study that examined the rate of successful diagnosis using 14-gauge biopsy needles found that obtaining 5 specimens was sufficient to diagnose 99% of cases of nodular breast lesions, but only 87% of microcalcifications, suggesting that more samples are needed for these lesions.31

Bleeding
Significant bleeding during the procedure may interfere with obtaining a successful biopsy of the lesion. It may be possible to determine whether blood vessels within the breast are at the same depth as the lesion. This may be accomplished by placing a target on the blood vessel in the stereo images, calculating the vessel depth, and comparing this to the calculated depth of the lesion.

Transfer to Pathology
Ensuring an accurate diagnosis requires close cooperation between the radiology team and the pathology team. The pathology team may have specific requirements for many aspects of the biopsy procedure, including the tissue delivery container, tissue fixation, and documentation.12

Underestimation of Disease
Inadequate tissue sampling may result in the failure to identify invasive breast cancer. The stereotactic biopsy results in the collection of fragmented samples of the target lesion, compared with surgical biopsy which removes the entire lesion.32 Studies that have compared the accuracy of percutaneous biopsy with surgical excision have found that needle biopsy is generally at least as accurate as surgery. However, there is the potential for the needle biopsy to undersample tissue. In these cases, the core biopsy specimen may be diagnosed as atypical ductal hyperplasia but contain carcinoma, or it may be diagnosed as DCIS even though the patient has invasive cancer.32 Underdiagnosis of breast cancer was evaluated in studies in which patients who were diagnosed with DCIS or atypical hyperplasia then underwent a subsequent surgical biopsy. They found that patients who were diagnosed with a biopsy diagnosis of DCIS or atypical hyperplasia are underdiagnosed in approximately 9% to 18% of cases.32,33

Patient Considerations
Before stereotactic biopsy, patients should be asked about allergies and about the use of any medications that may increase bleeding times, such as aspirin or anticoagulants. Other factors that may influence the appropriateness of the procedure include the patient's weight and ability to remain in the required position.17

As with any medical procedure, patients should understand that stereotactic breast biopsy is associated with both potential benefits and risks.20 Stereotactic biopsy is a rapid, simple, outpatient procedure that is usually not painful, and is generally as accurate as surgical biopsy. Unlike surgery, the needle biopsy does not distort breast tissue, which could interfere with the ability to read future mammograms. Potential harms of the procedure include the risk of bleeding and hematoma formation (especially with the vacuum-assisted biopsy, which removes larger tissue pieces), the risk of infection, the potential that the lesion might be missed, and the possibility that the extent of disease might be underestimated. There is a theoretical possibility that the needle sampling of the lesion might spread cancerous cells to surrounding tissues, although it is unknown whether this actually occurs. The diagnosis may be uncertain even if tissue is adequately sampled. Finally, although the procedure is generally very well tolerated by patients, some individuals will experience significant discomfort. Significant complications of needle biopsy are rare, and may include bleeding, vasovagal reaction, infection, and hematoma formation.16 Some temporary bruising is normal, but patients should be instructed to inform a healthcare professional if they experience excessive swelling, bleeding, drainage, or redness.16

Conclusions
Screening mammography significantly reduces the likelihood of mortality due to breast cancer, but most positive screening findings are not cancerous. Tissue biopsy is often essential in diagnosing breast cancer and planning treatment. Percutaneous biopsy procedures provide a less invasive alternative to surgical biopsy, with high accuracy and good patient comfort and convenience. Stereotactic biopsy uses pairs of 2-dimensional breast radiographs to calculate the distance of the target lesion beneath the skin, which may then be sampled using a variety of probe types, including core-needle biopsy or vacuum-assisted biopsy. Accurate tissue sampling requires consideration of several factors during the biopsy procedure, including patient selection and positioning, ensuring adequate breast thickness at the sample site to avoid negative stroke margin, patient anesthesia and skin preparation, and setting insertion depths for different biopsy devices. The procedure is generally safe and well tolerated by patients, and significant patient bleeding or discomfort is unusual.

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