PET, CT SCAN CRITERIA FOR BREAST CANCER

1. PET/CT for Patients With Breast
Cancer: Where Is the Clinical
Impact?
Sharma, Mohit Kumar
190966197

2. OBJECTIVE
• FDG PET/CT affects the management of patients with breast cancer in
multiple settings, including initial staging, treatment response
assessment, and evaluation of suspected recurrence. This article
reviews the strengths and weaknesses of FDG PET/CT for the staging
of the primary breast lesion, axillary and extraaxillary nodal
metastases, and distant metastases. The utility of FDG PET/CT for
measuring breast cancer treatment response is appraised and
compared with other imaging modalities. The role that tumor
histologic type may have on PET/CT interpretation is also discussed.

3. Performance of FDG PET/CT in Patients With
Breast Cancer
• The Society of Nuclear Medicine and Molecular Imaging guidelines contain
recommendations for patient preparation before FDG PET/CT to optimize
the distribution of FDG in the body and performance of the examination.
• The CT component of PET/CT is usually performed as a low-dose CT scan
with oral contrast agent but no IV contrast agent. At some centers and in
some cases, a full-dose CT scan with both oral and IV contrast agent may
be performed.
• The PET component of the PET/CT is usually reconstructed with a spatial
resolution of 5–6 mm full width at half maximum. Motion during image
acquisition can reduce this resolution. Detection of small lesions at PET
thus depends on FDG avidity, lesion size, and patient motion.

5. Initial Staging
• Clinical staging of breast cancer is based on the American Joint Committee
on Cancer’s TNM staging system, in which imaging plays a central role. All
patients with breast cancer should be assigned a clinical stage of disease,
because staging assists in determining local and systemic treatment and
provides prognostic information.
• Patients with locoregional breast malignancy have 5-year survival rates of
76–99%, but for those with distant metastases, this rate decreases to 20–
28% . Mammography, ultrasound, and breast MRI help accurately stage
local disease extent, whereas bone scan, abdominal CT or MRI, chest CT,
and FDG PET/CT play a role in systemic staging. Although it is not
appropriate for all patients with breast cancer, FDG PET/CT can have an
important clinical effect for appropriate patients.

6. The Primary Breast Tumor
• Dedicated breast imaging, including mammography, ultrasound, and breast
MRI, is the mainstay of evaluation of breast lesions. In comparison, whole-
body FDG PET/CT has low sensitivity for the primary breast tumor. Neither
FDG PET nor CT is sensitive enough to detect breast cancers smaller than 1
cm. Furthermore, several breast cancer histologic subtypes—most notably,
lobular breast cancers—have lower FDG avidity than the most common
ductal breast malignancies and may be occult at FDG PET even at large
sizes.
• Nuclear medicine evaluation of primary breast lesions has been improved
by the development of dedicated breast PET systems and dedicated single-
photon gamma imaging systems of the breast.
• Positron emission mammography has been found to be far more sensitive
than whole-body FDG PET/CT for the detection of primary breast
malignancies and additional ipsilateral breast tumors.

8. Locoregional Nodal Metastases
• For the purpose of evaluating the clinical utility of FDG PET/CT for breast
cancer locoregional nodal metastases, it is useful to make a distinction
between axillary and regional extraaxillary nodes. The mainstay of axillary
nodal staging for over 2 decades has been sentinel lymph node biopsy.
• Locoregional extraaxillary nodes, including internal mammary,
infraclavicular, and supraclavicular nodes, may be clinically occult and less
commonly identified by sentinel node evaluation. It is in this group of
nodes where FDG PET/CT evaluation begins to show value in patient
staging through the detection of unsuspected extraaxillary nodal
metastases. Identification of unsuspected extraaxillary nodal metastases by
FDG PET/CT at initial staging influences assignment of patient stage and
prognosis and may alter local therapy by altering the extent of local surgery
or radiotherapy

10. Distant Metastases
• Conventional imaging for distant metastases in patients with breast cancer
includes anatomic imaging with body CT and functional bone imaging by
methylene diphosphonate or similar gamma radiotracer bone scintigraphy
or 18F-NaF PET/CT. More recently, more-comprehensive functional imaging
with FDG PET/CT has been used. Extensive and growing evidence suggests
that FDG PET/CT identifies previously unsuspected distant metastases in
patients with locally advanced breast cance.
• The detection rate of unsuspected distant metastases by FDG PET/CT
increases as the pre-PET/CT local stage increases.
• The most common organ systems for distant metastases in patients with
breast cancer are bone, lymph nodes, liver, and lung [48]. There are several
FDG-avid tumor mimics in these organs that should be recognized and
distinguished from malignancy to increase the specificity of FDG PET/CT.

14. Treatment Response in Metastatic Disease
• The current standard of measuring treatment response in metastatic breast cancer relies
on size measurements of tumors, usually at CT. However, metabolic changes measured
by FDG PET may better predict treatment response than anatomic changes.
• Initial studies of FDG PET in the evaluation of breast cancer metastases found that FDG
PET could assess response versus nonresponse after only one to three cycles of therapy.
More recent studies found the ability to distinguish response from nonresponse, which
applied to distinct and varied courses of hormonal and chemotherapies.
• To date and to my knowledge, only one study has compared measuring metastatic
treatment response by CT and FDG PET/CT. Among 65 patients with metastatic breast
cancer, metabolic assessment by FDG PET/CT was a better predictor of both progression-
free and disease-specific survival than was Response Evaluation Criteria in Solid Tumors
evaluation at CT. Although further work is needed, this finding suggests that there is
incremental clinical value for FDG PET/CT in therapy response for patients with
metastatic breast cancer.

16. Does Receptor Status, Tumor Grade, or Histologic Type
Affect FDG PET/CT Interpretation?
• The term “breast cancer” actually comprises a wide range of biologically
different lesions, as classified by the World Health Organization. The most
common histologic types of breast cancer are infiltrating ductal carcinoma
(IDC), which accounts for 75–80% of primary breast malignancies, and
infiltrating lobular carcinoma (ILC), which accounts for 10–15% of primary
breast malignancies.
• Breast cancer grade is based on how much the cancer cells look like normal
cells, with a lower grade (1) implying that the cancer is more similar to
normal cells and a higher grade (3) indicating that the cancer is unlike
normal cells. The terms “well differentiated,” “moderately differentiated,”
and “poorly differentiated” are also used to depict grades of 1, 2, and 3,
respectively. Higher-grade malignancies usually grow more rapidly.

17. Clinical Effect
• Extensive retrospective and prospective evidence suggests that FDG
PET/CT detects unsuspected extraaxillary nodal and distant
metastases in patients with advanced local disease, with a greater
yield of detecting unsuspected malignancy at stage III (≈ 30% of cases)
than at stage IIB (≈ 10–15%).
• There is retrospective evidence that FDG PET/CT may better evaluate
treatment response than CT bone scan, the modality most commonly
used for measuring treatment response. Prospective evidence
suggests that FDG PET/CT is superior to CT bone scan for the
detection of malignancy in patients with suspicion of recurrent
disease [100]. Thus, FDG PET/CT affects the management of patients
with breast cancer in multiple clinical scenarios.

19. CONCLUSION
• Although FDG PET/CT is currently the PET modality with the greatest
effect on clinical management of patients with breast cancer, novel
radiotracers and imaging systems continue to broaden the application
of PET for patients with breast cancer. National Comprehensive
Cancer Network guidelines for FDG PET/CT for patients with breast
cancer are reviewed. Emphasis is given where FDG PET/CT has shown
clinical effect.

20. THANK YOU