Serum cyclophosphamide activity in patients treated for small cell carcinoma of the lung

Cyclophosphamide requires in vivo activation for its cytotoxicity. A bioassay of serum cyclophosphamide activity based on inhibition of normal peripheral blood CFU-C by serum from cyclophosphamide-treated patients was developed. Seventeen patients with small cell cancer of the lung were studied before and after cyclophosphamide administration in an attempt to correlate serum cytotoxicity in vitro with clinical response to chemotherapy. A correlation (r = 0.61, p less than 0.01) was discovered between serum cytotoxicity in vitro and subsequent leukopenia in vivo. However, a dose-response relationship was not found between serum cytotoxicity and response to chemotherapy. Besides drug dosage and blood level, other factors govern the sensitivity of small cell lung cancer to chemotherapy.