SPECT/CT boosts malignant lymph node detection in obese women

Multiplanar SPECT/CT lymphoscintigraphy provides better sentinel node detection in patients diagnosed with breast cancer than planar imaging alone, according to a study in the February issue of the Journal of Nuclear Medicine. The technique shows particular promise for overweight patients.

Minimally invasive axillary sentinel lymph node biopsy can make a noteworthy difference in the management of patients with breast cancer. Current data, however, suggest a significant association between body fat and the rate of false-negative exams. Researchers don't know the exact causes, but speculate that adipose tissue in the lymph nodes may compromise the test's accuracy. Obesity could thus lead to invasive, painful, and sometimes unnecessary full lymph node dissections.

Piling data show that planar approaches in nuclear imaging cannot successfully compete with tomographic multiplanar techniques. This study validates previous findings.

Multiplanar SPECT/CT could bring down the rate of failed biopsies, especially in overweight patients with breast cancer, said lead investigator Dr. Hedva Lerman, vice chair of nuclear medicine at Tel-Aviv Sourasky Medical Center in Israel.

"It also provides a more precise anatomical localization of the nodes prior to surgery, thus facilitating the surgical procedure," Lerman said.

Lerman and colleagues evaluated 220 consecutive women with invasive breast cancer who underwent sentinel node detection with three tests: an intraoperative blue dye technique, planar lymphoscintigraphy, and SPECT/CT lymphoscintigraphy.

The investigators also calculated patients' body mass indexes. BMI values of 18.4 Kg/m² or lower, 18.5 to 24.9 Kg/m², 25 to 29.9 Kg/m², and 30 Kg/m² and over were considered, respectively, underweight, normal, overweight, and obese. Of the 220 patients, 122 were overweight or obese.

Researchers found that SPECT/CT lymphoscintigraphy discovered sentinel nodes that were not identified with the other two techniques in a significant number of patients, particularly in overweight women.

Standard planar lymphoscintigraphy identified sentinel nodes in 78% of patients with an average BMI of 25 Kg/m² but failed to do so in 22% of patients with an average BMI of 28 Kg/m². SPECT/CT detected sentinel nodes in 91% of patients, including almost three times more sentinel nodes in overweight patients than did standard SPECT.

For the 122 overweight or obese patients, standard SPECT failed to identify sentinel nodes in 34 patients (28%). SPECT/CT failed to do so in 13 (11%). The difference was statistically significant (p<0.001). Of these patients, 116 underwent surgical biopsy. The intraoperative blue dye technique failed to detect sentinel nodes in 48 of these patients. Of these 48, SPECT/CT localized hot nodes in 36 (75%), while standard SPECT did so in 22 (46%).

Six out of 13 overweight and obese patients with negative scintigraphy and biopsy had nodal metastatic involvement. The finding suggests that beyond the technical limitations of any imaging technique, these patients should be approached with extreme caution, Lerman said. Her team will continue collecting data that help identifying sentinel nodes in challenging breast cancer subgroups and in patients with other tumors where nodal staging is indicated.

Adding SPECT/CT to the acquisition protocol in overweight and obese patients with breast cancer improves the identification of hot nodes and avoids false-positive reads. The technique provides particular value in patients for whom the identification of draining nodes by intraoperative techniques has failed, Lerman said.

"As the number of integrated hybrid SPECT/CT systems evolves, our results hopefully will encourage the use of lymphoscintigraphic SPECT/CT in other centers," she said.

For more information from the Diagnostic Imaging archives:

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SPECT/CT settles into variety of clinical practice settings

Nuclear medicine embraces MI applications

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