A novel 21-kDa protein as a serum marker for benign and malignant urogenital tumors: preliminary communication

A novel 21-kDa protein (p21) was isolated from auto-immune complexes, found in sera of 14 patients with malignant urogenital tumors and isolated on Protein A-Sepharose. Isolated complexes were analyzed in 15% polyacrylamide-SDS minigels. After staining with Coomassie blue R, the bands were scanned with a clinical densitometer. The level of p21 in sera of cancer patients was 3 times higher than that found in normal individuals. An attempt was made to correlate consecutive levels of p21 in the sera of these cancer patients with the clinical course. In 4 cases a significant decrease (57-75%) in the level of p21 was observed in parallel with response to treatment. In 9 of 10 cases where no response or tumor progression was observed, the relative abundance of p21 increased or remained unchanged. Thus, the level of p21 was indicative of progression or regression of the disease in 13 out of 14 patients. Similar high levels of p21 in sera were also found in 22 patients with benign hyperplasia of prostate. The p21 protein was not immunoreactive with known anti-ras antibodies such as Y13-259, 142-24E05 and anti-rap1. Partial amino acid analysis of this protein showed no complete homology to any known protein, but a partial homology to known bacterial proteins involved in DNA replication or transcription was observed. Monitoring of the novel p21 levels before and after treatment may be useful in follow-up of cancer patients, providing evidence of response to treatment.