The Usefulness of SPECT/CT in Sentinel Node Mapping of Early Stage Breast Cancer Patients Showing Negative or Equivocal Findings on Planar Scintigraphy.

Objectives: This study sought to determine the diagnostic yield of SPECT/CT in localizing axillary sentinel lymph nodes (SLNs) in early breast cancer patients where planar scintigraphy (PS) was equivocal or negative.

Methods: Prospective analysis of early stage breast cancer patients with non-palpable axillary nodes undergoing SLN localization prior to nodal sampling for axillary staging. PS findings were categorized as: Category A: non-visualization of SLN; Category B: unusual uptake location; Category C: equivocal uptake / difficult interpretation. The K-coefficient of Cohen was used to evaluate the correlation between PS and SPECT/CT results. PS and SPECT/CT images were interpreted separately, and SLN identification on each of the modalities was correlated to BMI (Body mass index) and peroperative radio guided results.

Results: Between April 2015 and January 2017, 1028 early breast cancer cases underwent sentinel lymphoscintigraphy. Of total, 134 (13%) patients underwent SPECT/CT in addition to PS. All were females with mean age of 48.15 years (range: 26-82 years). Right sided in 68, left in 64 and 2 with bilateral carcinoma. By TNM classification: 49 (37%) T1 , 78 (58%) T2 and 7 (5%) had DCIS/Paget's disease.Overall SLNs were detected on both PS and SPECT/CT in 60% cases. Of category A (n=54); 35/54 (64%) SLN localized on SPECT/CT; 32 were level-I; 2 Level-II; 1 Level-III nodes. In 19, SLN was not localized. Of category B (n=18), 5 had prior lumpectomy, SPECT/CT localized tracer uptake to 17 level-I sentinel nodes, 3 level-II and level III / IMC in 9. Of category C (n=62), 29 had prior lumpectomy. SPECT/CT confirmed SLN in all the cases. Radio-guided surgery confirmed SPECT/CT results. The correlation between the two techniques was low (K=0.34). Where PS was negative; SPECT/CT localized nodes in statistically significant number of cases (=0.01). PS identified SLN uptakes in 80/134 (60%) cases with a mean BMI of 21.6±4.8 kg/m2 while SPECT/CT detected ''hot'' nodes in 115/134 (86%) cases with a mean BMI of 29.6±5.6 kg/m2 . For overweight/obese patients (n=59) (BMI>25 kg/m2 ), PS failed to identify SLNs in 49 and SPECT/CT failed to do so in 18 (<0.001).

Conclusion: SPECT/CT has diagnostic yield and helps in precise SLN localization where planar imaging is negative or shows unusual site of uptake.