Modified ribonucleosides, derived predominantly from tRNA
and rRNA, are known to be excreted in abnormal amounts in
the urine of cancer patients (8, 11-18; for reviews see Refs. 1
and 19). These excretion products include specific methylated
nucleosides and pseudouridine (8, 16, 20, 21). Five urinary
modified nucleosides were evaluated by Waalkes et al. (8) as
potential tumor markers for patients with small cell carcinoma
of the lung, and the total frequency of elevated values for the
five nucleosides were reported to be directly related to stage of
disease.