Serum creatine kinase BB isoenzyme as a diagnostic aid in occult small cell lung cancer

Four patients with metastatic small cell carcinoma of the lung who had initial chest x-rays that did not reveal the cancer showed striking elevations of serum creatine kinase BB isoenzyme, which suggested the diagnosis and directed the subsequent evaluation. Creatine kinase BB isoenzyme elevation with widespread small cell carcinoma of the lung is probably more common than currently recognized, and is a useful diagnostic indicator for extensive stage small cell lung cancer, even in the absence of central nervous system metastases.