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PET/CT and a subcentimeter lesion in breast cancer
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A 43-year-old woman was referred to our hospital with history of left breast multifocal ductal carcinoma in situ for which she underwent bilateral mastectomy and reconstruction in 2006. Her family history was significant for breast cancer: Her sister was diagnosed at age 38, maternal aunt at age 36 and maternal cousin at age 25. All died from metastatic disease. She was positive for BRCA2 mutation, at which time she opted for left mastectomy and prophylactic right mastectomy. She now presents with palpable mass in the left axilla and underwent an FNA of the mass, which showed moderate cellularity composed of polymorphous population of lymphocytes, predominately small lymphocytes, with no evidence of malignant cells. She later underwent an ultrasound of the left axilla that showed a 2.7 cm × 2.2 cm × 0.9 cm lobulated mass representing lymph node with an echogenic fatty hilum.
A core biopsy of the left axillary lymph node showed adenocarcinoma with ER 90% positive, PR 50% positive, HER2-neu2 positive by immunohistochemistry and negative by fluorescent in situ hybridization and E-cadherin positive. A staging PET/CT showed a hypermetabolic 16 mm × 7 mm left axillary lymph node with maximal SUV of 2.7 and superiorly, there was a smaller lymph node measuring up to 8 mm × 5 mm with maximal SUV up to 1.1. There were no suspicious lesions in the breast or contralateral axilla, or systemically.
She will undergo axillary lymph node dissection, systemic chemotherapy and possible radiation.
Discussion
FDG-PET imaging has 88% sensitivity and 80% specificity for primary breast lesion, 61% sensitivity and 80% specificity for axillary metastases, and 93% sensitivity and 79% specificity for metastatic disease. Sensitivity and specificity is further improved with simultaneous CT acquisition and image fusion of PET and CT images.
During the past few years, with improvement of spatial resolution of PET, we have been able to achieve a system resolution of 5 mm to 6 mm under optimal clinical conditions. However, PET is still limited by small size of the lesion and in general the sensitivity to detect malignant lesions decreases with lesions <1 cm in breast tissue and axillary metastasis. Sentinel node sampling is shown to be approximately 20% more sensitive in detection of regional lymph node metastases from breast carcinoma.
However, it is important to note that in the appropriate clinical setting, the presence of metabolic activity in the subcentimeter lymph nodes should be considered suspicious for metastatic disease, unless proven otherwise.
 Figure 1: Axial PET/CT image demonstrates hypermetabolic activity corresponding to the biopsy-proven recurrent breast carcinoma in the left axilla. Upper left image is axial CT scan, upper right image is corresponding PET image, lower left image is fusion image containing PET images displayed on a color scale and CT images displayed on a gray scale. Lower right image is maximum intensity project (MIP) image of whole body PET study. |
 Figure 2: Axial PET/CT image slightly craniad to Figure I demonstrates hypermetabolic activity associated with subcentimeter left axillary lymph node. Display convention is the same as Figure 1. Courtesy of M Ghesani |
In this patient, for example, it is very likely that the smaller subcentimeter lymph node with associated metabolic activity is involved with metastatic disease even though it does not meet the standard CT criteria for metastatic disease. We will soon have histopathology correlation once the patient undergoes axillary lymph node dissection.
There is ongoing research with newer techniques to improve detection and render better staging of breast malignancy such as newer high-resolution, high-sensitivity positron emission mammography (PEM) with either a combining dedicated CT or dynamic contrast-enhanced MRI.
The above case illustrates the importance and significance of FDG uptake in the subcentimeter lymph nodes for positive disease while the absence of FDG uptake does not rule out disease due to resolution limitation of PET/CT.
For more information:
- Frangioni JV. J Clin Oncol. 2008;26:4012-4021
- Rosen EL. Radiographics. 2007;27:S215-S229.
- Weber WA. J Clin Oncol. 2006;24:3282-3292.
- Vamsee Torri, MD, is a Fellow in Hematology/Oncology at St. Luke’s-Roosevelt Hospital Center.
- Sharon Rosenbaum Smith, MD, is Attending Breast Surgeon at St. Luke’s-Roosevelt Hospital Center.
- Munir Ghesani, MD, is Associate Clinical Professor of Radiology at Columbia University College of Physicians and Surgeons and Attending Radiologist at St.Luke’s-Roosevelt Medical Center.