Plasma sarcosine does not distinguish early and advanced stages of prostate cancer
The original publication is available at http://www.samj.org.za
Introduction. Diagnosis of prostate cancer by prostate specific antigen (PSA) is error-prone and cannot distinguish benign prostatic hyperplasia (BPH) from malignant disease, nor identify aggressive and indolent types. Methods. We determined serum sarcosine (N-methylglycine) in 328 cancer patients by gas chromatography (GC)/mass spectroscopy (MS) and searched for correlations with early (stage T1/T2) and advanced (stage T3/T4) disease. Results. Serum sarcosine of male control patients ranged from 1.7 μmol/l to 4.8 μmol/l. In prostate cancer patients, sarcosine ranged from 2.8 μmol/l to 20.1 μmol/l. Expressed as the sarcosine/alanine ratio, serum control values were 9.4±5.5x10 -3 (mean±SD) compared with 21.6±9.0; 28.5±16.6; 22.7±7.7 and 22.2±11.0 for patients diagnosed with T1, T2, T3 and T4 prostate tumours, respectively. The small differences between T1, T2, T3 and T4 patients were not statistically significant (p=0.51). However, the conventional PSA marker significantly correlated with T stage in these patients (r=0.63; p<0.009). Conclusions. The median sarcosine/alanine ratios among patients with early and advanced prostatic cancer ranged from 21.6±9.0 to 28.5±16.6 and were fairly constant, showing no statistically significant differences between T-stages. The results are consistent with published data in urine and serum which find differences between controls and patients with metastatic prostate cancer to be small and sarcosine to be uninformative regarding prostate cancer progression. By multi-comparison of PSA with T-stages in the same group of patients, we found significant correlations confirming the well-known merits and limitations of this marker.