Breast Cancer

Fast Facts:

• 30% of all cancers in women.
• 2nd leading cause of cancer death for women.
• 12% of women will develop invasive breast cancer.

Indications for PET/CT Scan:

Diagnosis: Currently, no role in either screening or diagnosis.

• Dual-Point Imaging: Some advocate imaging breast lesions at both 1-hour and 2-hours.  Malignant lesions are generally thought to increase their FDG uptake over time, while benign lesions do not.  

Initial Staging: Permits both assessment of initial disease and serves as a baseline exam for follow up reference.

• Patients with locally advanced disease.
• Cases where conventional imaging results are equivocal.
• High likelihood of metastatic disease at presentation.
• When neoadjuvant chemo and/or radiation is contemplated.
• Inflammatory breast carcinoma
• Triple negative breast cancers

Assessing Response to Therapy & Prognosis: 

• Early Response: Non-responders can be offered alternative therapy.
• Late Response: Assess success or failure of therapy, and ultimate outcome.

Recurrence & Restaging: 

• Restaging suspected recurrence (clinically or rising tumor markers).
• Distinguishing recurrence from post-therapeutic inflammation/scarring.

Additional Strengths of PET/CT:

• Mediastinal, supraclavicular and internal mammary lymph nodes status.
• Detecting distant metastatic disease.
• Detecting multi-focal or multi-centric breast disease at presentation.
• Assist surgical planning.

Limitations:

• Does not replace sentinel lymph node biopsy or axillary nodal dissection for the initial evaluation of axillary nodal status.
• Not recommended for routine post-therapy surveillance.

Criteria for “Active Malignancy”: 

Nearly every breast cancer patient presenting for PET/CT imaging already has a biopsy-proven diagnosis. Occasionally, however, an incidental breast cancer is found.

• Any focus of metabolic activity (well-defined or not) above mediastinal blood pool should raise a suspicion for malignancy.  [Case 1 ]
• An accompanying well-defined soft tissue abnormality will not always be detected on the co-registered CT images, particularly if the patient has dense breast parenchyma.
• The more focal the lesion and the more intense its uptake, the more likely the lesion is to be malignant.
• The presence of associated hypermetabolic nodes dramatically increases the likelihood of malignancy.

What We Report:  

Size, metabolic activity & location of the primary lesion and representative metastatic lesions.  [Cases 1-8 ]

• Primary Lesion: Size, metabolic activity & location (can be multifocal).
• Loco-Regional Disease: Hypermetabolic lymph nodes and chest wall invasion are the most common findings.  
• Distant Disease: Most commonly to the bones, lung, brain, liver and adrenal glands.

False Positives:

• Inflammation (infection, post-surgical, post-traumatic).
• Heterogeneously glandular breasts can occasionally demonstrate mild, focal areas of FDG uptake.
• Benign breast lesions: On rare occasion, benign lesions such as ductal adenomas and fibroadenomas can be FDG-avid.  
• Reactive bone marrow secondary to chemotherapy and/or colony stimulating factors can mimic diffuse skeletal metastases (addressed in detail, here).
• “Flare Phenomenon”: 
  • Osteoblastic activity associated with healing of bone lesions can lead to an increase in their metabolic activity on a follow-up scan (one may also see an increase in the number of FDG-avid bone lesions, as an occult lesion on the prior exam now becomes apparent).
  • Typically occurs 2 weeks to 3 months after therapy (can be as late as 6 months).
  • Consider this possibility when the patient’s osseous metastatic disease appears worse, yet the non-osseous findings have improved.  In such cases, recommend follow-up. 
  • Associated most frequently with breast, prostate and NSCLC.

False Negatives:

• Low-Avidity Cancers: Lobular carcinoma, carcinoma-in-situ, tubular carcinoma, ER-Positive cancers.
• Lesions less than 8.0 mm: These very small lesions may have minimal or no appreciable uptake, as they are “beneath the resolution of PET”.
• Axillary Nodes: Even minimal FDG-uptake in axillary nodes — in the setting of an ipsilateral breast cancer — should be considered suspicious for metastatic disease (for this reason, PET/CT does not replace sentinel lymph node biopsy or axillary nodal dissection for the initial evaluation of axillary nodal status).
• Internal Mammary Nodes: As the majority of metastatic internal mammary nodes are less than 8.0 mm in size (“beneath the resolution of PET”), even minimal activity in these nodes is highly suspicious for metastatic disease.  [Case 2]
• Sclerotic Bone Metastases:
  • While PET/CT imaging is clearly superior to convention bone scanning for lytic and mixed lytic/sclerotic lesions, it has traditionally been considered less sensitive than a conventional bone scan for blastic lesions.
  • Recent literature, however, suggests that while a bone scan may be more sensitive than a PET scan alone for blastic lesions, it may actually be less sensitive when compared to a PET scan plus a CT scan (e.g. a PET/CT scan).

Reporting Language:

Clinicians (and patients) are hoping to see the following language as the Impression of your reports: “There is no convincing evidence of FDG-avid local, regional or distant breast carcinoma.”