Tc-99m depreotide SPECT/CT for lymph node staging of non-small-cell lung cancer

To investigate the potential role of Tc-99m depreotide (Tc-DEPR) in the preoperative lymph node (N) staging of non-small-cell lung cancer (NSCLC).

Sixty-one patients with NSCLC at the potentially operable stage were enrolled and underwent scintigraphy before surgery (n = 56) or mediastinoscopy (n = 5). Imaging was performed with a hybrid single photon emission computed tomography/computed tomography (SPECT/CT) system. Depreotide uptake in N stations was evaluated visually and semi-quantitatively and compared to histology. Quantification was carried out in attenuation-corrected SPECT slices. Different sites of normal uptake were used as a reference for comparison with lesional uptake. Receiver operating characteristic analysis was employed to identify the most preferable reference area and the cut-off best discriminating disease-free from disease-involved lymph nodes.

With reference to 53 Ν1 hilar and 147 Ν2/Ν3 sampled stations, sensitivity of scintigraphy by visual interpretation was 100 and 94 %, specificity 43 and 59 % and accuracy 55 and 67 %, respectively. No patient was down-staged, but 52 % were incorrectly up-staged and 44 % were misclassified as inoperable. Compared to scintigraphy, preoperative contrast-enhanced diagnostic CT demonstrated lower sensitivity (36 % for hilar and 73 % for N2/N3 stations), higher specificity (79 and 75 %) and similar accuracy (70 and 75 %). Regarding the ultimate N-stage and the prediction of surgical disease, diagnostic CT was wrong in 51 and 34 % of cases. Dichotomy of quantitative scintigraphic data by the use of certain N-to-spine ratio cut-offs resulted in a significant increase of specificity (76 % for hilar and 89 % for N2/N3 stations), while sensitivity remained high (82 % in both circumstances) and accuracy for Ν2/Ν3 stations was substantially improved (88 %). By this quantitative approach, misclassifications as to the N-stage and patient operability (25 and 16 %) were considerably less than that of visual Tc-DEPR and diagnostic CT interpretations.

Tc-99m depreotide SPECT/CT seems to have a role in the N-staging of NSCLC, mainly because of its high sensitivity and negative predictive value. Quantification of uptake can improve specificity, at a low cost of sensitivity. If F-18 fluoro-deoxyglucose positron emission tomography is not available, this method may be used as a surrogate to conventional staging modalities.