Purpose: Tc-99m depreotide is a peptide analogue of a somatostatin receptor that preferentially binds to somatostatin receptors 2, 3, and 5. Many lung tumors may express these receptors to a greater extent than normal tissue. Tc 99m depreotide study is a noninvasive, receptor-specific imaging agent that is used to assess malignant versus benign single pulmonary nodules before biopsy.
Materials and methods: Thirty-nine consecutive patients (15 men, 24 women), with mean age 56.6 years (range 39-86) underwent 42 studies. The single-photon emission computed tomographic scan of the chest and whole-body imaging were performed 2 hours after intravenous injection of Tc 99m depreotide (average dose, 24 mCi). The region of interest was drawn around each lesion, and the tumor-to-background ratio was measured. Images were classified as true positive when the tumor uptake and histopathology were concordant. The results were classified as true negative when there was no uptake in the absence of malignancy. The results were classified as false positive when there was uptake in areas other than tumor and were false negative when no uptake in the tumor was identified. The computed tomographic and pathological correlations were performed.
Results: The comparison of technetium Tc 99m depreotide imaging with computed tomographic study revealed a sensitivity of 1.0 versus 0.9, a specificity 0.43 versus 0.19, accuracy 0.71 versus 0.55, positive predictive value 0.64 versus 0.53, and negative predictive value 1.0 versus 0.67,. The tumor-to-background ratio ranged from 1.15 to 3.77. There was no relationship between the histology and the intensity of tumor uptake. The tumor uptake was high in sites of acute and active inflammation.
Conclusion: Technetium Tc 99m depreotide imaging is a sensitive imaging modality with better specificity and negative predictive value than computed tomography. There is no relationship between tumor uptake and differentiation of the tumor. We recommend a technetium Tc 99m depreotide study forthe evaluation of solitary pulmonary nodules, especially when positron emission tomography is not available before biopsy.