Tc-99m depreotide detecting malignant pulmonary nodules: histopathologic correlation with semiquantitative tumor-to-normal lung ratio.

Tc-99m depreotide is a synthetic somatostatin analog with a low molecular weight of 1358 and binding domains for somatostatin receptors (SSTRs) subtypes 2, 3, and 5. This agent has been used for imaging pulmonary nodules in an effort to differentiate malignancies from infectious processes. To investigate whether there is significant ratio variability predicting a specific lung cancer type, we undertook this study. We analyzed the semiquantitative tumor-to-normal lung ratios among 23 patients with histopathologically proven lung carcinoma. Eleven patients with squamous cell carcinoma had 14 nodular lesions (n = 14); the ratios ranged from 6.0 to 1.4; the mean was 3.500. Nine patients with adenocarcinoma had 9 nodular lesions (n = 9); the ratios ranged from 3.2 to 1.0; mean was 1.89. Three patients with large cell carcinoma had 3 nodular lesions (n = 3); mean was 1.2. There were significantly different ratio values between squamous cell carcinoma and nonsquamous cell carcinoma. On a statistical analysis by t test, this difference proved to have a statistically significant value of P < 0.038. For patients with lung cancer, we could predict the tumor most likely to be squamous cell carcinoma if the uptake ratio was greater than 3.5. Otherwise, the lower ratio appeared to be either the result of large cell carcinoma or adenocarcinoma. High tumor uptake of Tc-99m depreotide reflecting abundant SSTRs of a tumor and/or peritumoral neovasculature such as squamous cell carcinoma could be potentially useful in diagnostic and therapeutic guidance.