Breast PET Imaging and Axillary Node Evaluation

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The occurrence of axillary metastases plays a major role in therapeutic decisions for management of newly diagnosed breast cancer patients. Surgical treatment, radiation therapy decisions and chemotherapy usage are greatly influenced by the presence or absence of breast cancer that has spread to the axillary lymph nodes. The gold standard for identifying node involvement is microscopic confirmation of excised tissue. Sentinel node biopsy is our most common approach to identifying the spread of disease, but more frequently we are seeing preoperative axillary assessments.

The pre-surgical evaluation of nodal status includes physical exam and standard imaging with combinations of ultrasound, mammogram and MRI. FNA or core biopsies directed by these findings can provide valuable information.  Breast PET imaging can also be used to evaluate the axillary lymph nodes for metastatic disease. Breast PET imaging also brings metabolic information into the decision process so that it is more accurate than mammogram and ultrasound. The false positive rate (thinking a lymph node contains cancer when it does not) using breast PET was 1%, compared to a 22% false positive rate noted on ultrasound evaluation alone.

A standard breast PET imaging protocol involves intravenous injection of 5 mCi of 18F-FDG followed by a one hour wait for uptake of tracer by malignant cells. Tomographic images of the breasts and the axilla of the involved breast are obtained. With a positive axillary finding, ultrasound evaluation is initiated with needle biopsy of any findings. If a negative ultrasound is encountered or if the biopsy is negative for metastatic disease, then the patient proceeds on to a sentinel node biopsy. A confirmed nodal metastasis requires a decision to proceed on with surgery or to undergo neoadjuvant chemotherapy prior to surgical intervention. The final post-surgical nodal results will influence radiation decisions to the axilla and chest wall.

A group of newly diagnosed cancer patients from 2014 were studied. Breast PET imaging showed a low sensitivity of 48%, but acceptable specificity, positive and negative predictive values (99%, 93% and 89% respectively). Also, the false positive rate was only 1%.

Limitations of breast PET imaging include the ability to detect disease less than 6 mm in size. Lobular breast cancer metastases also appear to be more difficult to detect on breast PET. Nearly 25% of the undetected lesions on breast PET imaging were lobular cancers. Methods to improve detectability such as system geometry and post reconstruction algorithms are being investigated. 

With the current data showing a high specificity and low false positive rate, indications are that breast PET can play a crucial role in pre-surgical axillary assessment. This information will guide decisions regarding neoadjuvant chemotherapy and the use of sentinel node biopsy or axillary node dissection. 

Case Study:

  • 52 year- old female with bilateral IDC
  • High Resolution Breast PET with axilla views 
  • Left lesion and 3 suspicious lymph nodes
  • L-ALND confirms 3/13 + nodes
  • Right  lesion and no suspicious lymph nodes
  • R-SLNB confirms 0/2 + nodes.

Left_MLO.jpgLeft MLO    Left_Axillary_View.jpgLeft Axillary View

Right_MLO.jpgRight MLO    Right_Axillary_View.jpgRight Axillary View

Images Courtesy Dr. Michael Kinney, The Center for Advanced Breast Care, Arlington Heights, IL