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Breast Cancer Diagnosis How Technology Fits In |
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By Harriet Borofsky, M.D.
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This
year marks my tenth anniversary as imaging director of The Breast Center
at Mills-Peninsula Health Services. As I reflect on these years, I am
humbled by the challenge and difficulty in detecting breast cancer early.
Rapidly evolving technologies and interventional procedures have
transformed the role of the breast radiologist from isolated consultant to
integral part of the multidisciplinary team caring the many women
diagnosed with breast cancer. With minimally invasive core needle biopsy
of the breast replacing surgical excisional biopsies as standard of care
in breast diagnoses, it is often the breast radiologist who is the first
to share with a woman that intensely personal and life-altering diagnosis
of breast cancer. The demanding nature of
early detection and diagnosis of breast cancer along with the known
limitations of film-screen mammography, which has a false-negative rate of
10 percent to 20 percent, have driven rapid advances in new technologies
in breast imaging in the hopes of improving our detection and diagnostic
accuracy. Despite these exciting and promising advances, mammography
remains the primary imaging modality for evaluation of breast diseases and
remains the only imaging modality proved to be efficacious in the early
detection of breast cancer. Randomized controlled trials have demonstrated
mortality reductions from breast cancer in women screened to be in the 30
percent to 44 percent range. New technologies
playing an increasingly important role in breast imaging include digital
mammography, computer-aided detection (CAD), PET, ultrasound, and magnetic
resonance imaging of the breast. Digital Mammography Full-field digital
mammography (FFDM), which is rapidly replacing film-screen mammography,
was introduced in prototype form in 1996 and approved for clinical use by
the Food and Drug Administration in 2000. The basis for this technology is
the replacement of the fluorescent screen and film used in standard
screen-film mammography with a digital detector that can record X-rays as
electrical signals that are converted to digital data, processed in a
computer, and interpreted in soft copy form from high-resolution monitors.
This technology allows post-processing of the image to maximize
brightness, soft tissue contrast, and resolution. Digital mammography
eliminates the image variability and noise inherent in film processing. It
is the hope that these properties will enable digital mammography to
detect cancers that might be missed with film-screen mammography,
especially in the dense breast. Additional benefits
include decreased radiation dose to the patient and markedly improved
efficiency of exam time and patient throughput. Once captured, the digital
image is instantaneously transferred to a reading station, which may be
on- or off-site, to be interpreted from computer monitors and stored in
picture archiving and communication systems (PACS). Digital technology is
not without its drawbacks and limitations. The trade-off of better
contrast resolution with digital imaging is the slightly diminished
spatial resolution (ability to discriminate tiny objects or
calcifications) compared with film-screen mammography. Both are essential
in detecting early breast cancer. Digital mammographic units with computer
monitors are much more costly than film-screen units, which prohibit their
use in many facilities. In addition, the clinical efficacy of digital
mammography is still under investigation. A recently published Swedish
study comparing 25,263 women, 45 to 69 years of age, randomized to be
screened with film-screen vs. digital mammography showed a slightly
improved cancer detection rate with digital mammography, although not
statistically significant, with a decreased dose to the breasts and an
increase in recall rate.1
An eagerly anticipated multi-institutional study, the ACR Imaging
Network Digital Mammographic Imaging Screening Trial (ACRIN), will compare
49,5000 women screened with digital vs. film-screen mammography in 28
centers in the United States and Canada and is soon to be published. Computer-Aided Detection (CAD) Along with digital
technology have come propriety computer software programs that use
algorithms to review mammograms for findings that might be indicative of
breast cancer. These computer-aided detection systems, known as CAD,
digitize and analyze a mammographic image to highlight regions of interest
and simulate a double reading with the goal of reducing false-negative
interpretations. A recent study by Freer
et al., performed in a community setting, showed an increase in
cancer-detection rate of 19.5 percent and an increase in early, stage 0
and 1 breast cancers, detected from 73 percent to 78 percent after
implementing CAD to their screening program.2 CAD technology,
however, is limited by its low specificity; nearly 98 percent of CAD marks
are appropriately dismissed by radiologists, and by its limited
sensitivity. Nine out of 49 cancers, in the Freer study, were not marked
by CAD but were detected by the interpreting radiologist. PET Positron emission
tomography (PET) is an advanced imaging tool for diagnosis, staging, and
restaging of certain cancers. Its main role in breast cancer is in the
evaluation for metastatic disease in women presenting with advanced
primary tumors or in women with recurrent tumors for restaging evaluation.
PET has NOT been shown to be useful in estimating tumor biologic behavior,
in determining extent of disease in the breast, or in determining axillary
lymph node status. Breast Ultrasound Dedicated breast
ultrasound is probably the most valuable adjunctive imaging modality in
breast evaluation. Its uses and indications are rapidly evolving with
recent technologic advances in high-resolution transducers and real-time
scanners. Traditionally used as a targeted exam mainly to differentiate a
cyst from solid nodule, indications for breast ultrasound now include the
work-up of questionable or nonspecific mammographic finding, evaluation of
patients presenting with lumps, focal pain, nipple discharge, and enlarged
axillary lymph nodes and as the initial imaging evaluation in symptomatic
women pregnant or younger than 30 years of age. The role of breast
ultrasound in the adjunctive screening setting is evolving and remains
controversial. Ultrasound is being increasingly used as second-level
screening for high-risk women and for women with dense fibroglandular
tissue, in whom the sensitivity of mammography is limited. It is also
being used in presurgical staging evaluation of women newly diagnosed with
breast cancer to evaluate for multifocal and multicentric disease and
axillary metastases and to evaluate for malignancy in the contralateral
breast. Breast ultrasound may detect additional multifocal or multicentric
disease in 14 percent of newly diagnosed breast cancer patients and may
detect contraleral disease in 4 percent.3
A widely publicized and compelling 2002 study by Kolb et al. performed
adjunctive screening ultrasounds in more than 12,000 women with dense
fibroglandular tissue and normal mammograms and found an increase in the
cancer detection rate by 13 percent with 89 percent of additional
ultrasound-detected cancers to be early stages 0 and 1.4
Magnetic Imaging of the Breast (MRI) Magnetic resonance
imaging (MRI) of the breast is well established as the imaging modality of
choice in the evaluation of silicone breast implants for rupture. Its role
in breast cancer detection is rapidly evolving with the advent of new
dedicated breast coils, dynamic imaging sequences, and increasing
availability in performing MRI-guided breast biopsies. MRI offers the
distinct advantage of combining physiologic as well as morphologic
assessment of breast findings as malignant invasive tumors enhance in a
characteristic way following bolus administration of intravenous contrast
because of tumor angiogenesis and neovascularity. MRI imaging of the
breast is a cross-sectional imaging modality not limited by overlapping
structures or by the density or complexity of the fibroglandular pattern. MRI is extremely
sensitive in detecting most invasive breast cancers, greater than 90
percent. However, its sensitivity in detecting DCIS is low, approximately
40 percent in most studies; and its specificity for malignancy is limited,
varying in studies from 39 percent to 95 percent. Contrast enhancing
lesions, although associated with malignancy, may commonly be seen in many
benign breast findings and during certain phases of the menstrual cycle. The role of MRI of the
breast is rapidly evolving along with clinical experience. Several recent
studies have shown that in staging evaluation of newly diagnosed breast
cancer, MRI can detect additional ipsilateral disease in 27 percent of
cases5
and can detect additional contralateral disease in 4 percent to 5 percent
of cases.6 In high-risk
women, on the basis of family history or genetic predisposition with BRCA
mutations, MRI has been shown to detect mammographically occult breast
cancer in 2 percent to 8 percent of patients. A recent highly publicized
study published in the New England Journal of Medicine last summer
compared clinical breast exam, mammography, and breast MRI in 109
high-risk women with familial or genetic predisposition and found MRI to
have a sensitivity for detecting breast cancer of 95 percent as compared
with mammography and clinical breast exam, which had sensitivities of 33
percent and 18 percent respectively.7
The American Society of
Breast Disease issued a policy statement, July 2004, based on reported
literature regarding appropriate indications for use of breast MRI to be
as follows: •
for preoperative staging evaluation of newly diagnosed breast
cancers, • for adjunctive screening in high-risk women on the basis of familial or genetic
predisposition, • for detecting occult breast cancer in women presenting with axillary nodal
metastases, •
for monitoring response to neoadjuvant chemotherapy, •
for distinguishing post-operative scarring from tumor recurrence, •
for evaluation of silicone breast implants for rupture. It should be noted that
there are no studies to date evaluating the role of breast MRI in
population-based screening. MRI is not indicated in the evaluation of
mammographically or sonographically detected lesions that should otherwise
undergo biopsy. Ongoing clinical trials and clinical experience will
certainly expand the role of MRI in breast imaging in the future. Summary The specialty of breast
radiology requires expertise in these multiple imaging modalities of
radiography as it evolves to digital imaging, cross-sectional imaging with
expanded utilization of ultrasound and MRI, nuclear medicine with PET, and
interventional procedures. Despite the promise and
excitement in these new technologies, no single imaging study or
combination of studies can guarantee that a woman does not have or will
not be diagnosed with breast cancer. These new technologies however will
definitely improve our detection and diagnostic capabilities and will
certainly have a positive impact on the many women whose lives are
affected by this disease. Dr.
Borofsky is a radiologist in San Mateo and is medical director of the
Breast Center at Mills-Peninsula Health Services.
Endnotes: 1
Oslo II Study; Radiology 2004; 232: 197-204. 2 Freer et al. Screening Mammography with CAD: Prospective Study in a
Community Breast Center. Radiology. September 2110: 781-786. 3 Moon et al. Multifocal, Multicentric and Contralateral Breast Cancers: Bilateral
Breast
US in Preoperative Evaluation of Patients. Radiology,
2002: 569-576. 4 Kolb et al. Comparison of the Performance of Screening Mammography, Physical
exam and Breast US in Detection of Breast Cancer. Radiology,
2002: 165-175. 5 Liberman et al. MR Imaging of the Ipsilateral breast in Women with Percutaneously
Proven Breast Cancer. AJR 2003; 180: 901-910. 6 Liberman et al. MR Imaging Findings in the Contralateral Breast of Women with
Recently Diagnosed Breast Cancer. AJR 2003; 180: 333-341. 7 Kriege et al. Efficacy of MRI and Mammography for Breast Cancer Screening in Women with a Familial or Genetic Predisposition. New England Journal of
Medicine, 2004. 351: 427-437.
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