INCREASED LEVELS OF A 21-KDA PROTEIN IN THE CIRCULATION OF TUMOR-BEARING PATIENTS

A novel non-ras 21-kDa protein (p21) was detected in sera of cancer pa tients by enzyme-linked immunosorbent assay (ELISA), using polyclonal anti-p21 antibodies. While only 4.6% of the healthy donors (n = 43) sh owed p21 serum levels higher than the mean +/- 2 SD of the normal grou p, 33 to 80% of the cancer patients (n = 94) with various tumors were positive in the ELISA test. In particular, patients with malignant lym phoma, urogenital, and gastrointestinal tumors had a 2.8- to ninefold increase in p21 serum levels. Elevated serum levels were also found in patients with benign prostatic hyperplasia (3.2-fold increase). In 17 out of 22 patients with urogenital tumors, changes in serum p21 level s correlated with the clinical course of the disease. In 15 patients, a favorable response to therapy was correlated with a decline in serum p21 level. Two patients with renal cell carcinoma showed increased or persistently high levels of p21 after surgery and were subsequently f ound to have distant metastases. Expression of p21 in ten renal cell c arcinoma tissues was determined by Western blotting. There was a trend toward a higher content of p21 in the less-differentiated tumor tissu es. In conclusion, p21 may be a useful indicator in monitoring the out come of treatment in patients with various malignant tumors. In patien ts with renal cell carcinoma. p21 serum levels may be of particular im portance because no other tumor marker is available.