Fast cancer uptake of Tc-99m-labelled bombesin (Tc-99m BN1)

In human blood, breakdown of gastrin-releasing peptide and other bombesin-related peptides occurs in less than 15 min. This quick enzymatic cleavage might impair the diagnostic use of labelled bombesin (BN). Tc-99m-labelled bombesin (Tc-99m BN1) was injected intravenously and dynamic uptake data were acquired for diagnosing 26 cancers of different origin: 15 breast, 3 prostate, 5 colo-rectal, I pancreas, 2 small cell lung cancers and I gastrinoma. Background subtracted tumour uptake data were plotted against time and fitted with known mathematical functions. Twenty-three out of 26 cancers showed rapid increase of radioactivity followed by a radioactivity plateau, with some oscillations around the average plateau value. The time to 80% of max activity (T-80) was the reference parameter to measure and to compare the uptake speeds. The slowest T-80 was 7 min in one T1b breast cancer, gastrinoma reached T-80 in 5 min and node-positive prostate cancers in 2 min. N+ breast cancers showed T-80 at 3.62 +/- 0.75 min, N-breast cancers at 5.5 +/- 0.88 min (p<0.02). When all the tumours were considered, N+ tumours showed T-80 at 2.68 +/- 1.03 min and N-cancers at 5.5 +/- 0.82 min. In all the cancer types, the uptake of Tc-99m BN was faster than 10 min. This result shows the ability of Tc-99m BN to image tumours. The faster uptake by N+ versus N- cancers probably depends on the higher blood flow in N+ cancers.