Faculty Bibliography

Widespread application of intralesional tritiated thymidine injection to obtain cell kinetic data in lung cancer is described. Thymidine-labeling indices were obtained in 28 patients with lung cancer, and the data analyzed by histologic cell types. The mean and median labeling indices were highest in small-cell carcinoma of the lung. Mean values were significantly higher in the small-cell and in the large-cell undifferentiated carcinoma groups than in the adenocarcinoma and epidermoid carcinoma. On the other hand, a labeled mitosis curve in a patient with small-cell carcinoma yielded a duration of DNA synthesis of 18.8 h; not unlike those obtained for other solid tumors. According to our concepts of tumor growth, these findings suggest that the fraction of proliferating cells may be significantly higher in the small-cell and large-cell undifferentiated carcinomas than in the more differentiated cell types of bronchogenic cancer. Knowledge of the growth fraction of these cancers may have implications in directing therapeutic approaches and in interpreting features of the natural history of the disease.