Clonogenic growth in vitro: an independent biologic prognostic factor in ovarian carcinoma A retrospective analysis was performed to investigate the prognostic value of growth in a human tumor clonogenic assay system for 84 ovarian cancer patients. A significant difference in survival probability (determined by the method of Kaplan-Meier) was found by univariate analysis between patients with ovarian carcinoma whose tumors manifested clonogenic growth (defined as growth of greater than or equal to five colonies per plate) and patients whose tumors did not grow. Clonogenic growth in vitro was associated with worse prognosis (P = .007, log-rank test). A number of generally accepted prognostic factors, International Federation of Gynecology and Obstetrics (FIGO) stage (P = .003), residual tumor mass (P less than .001), and grade (P = .011), were also of prognostic importance in our patient population. Multivariate analysis, based on the Cox regression model, identified clonogenic growth as a significant independent prognostic parameter in ovarian carcinoma (P = .031), in addition to the conventional risk factors. Estimation of survival of individual patients was best accomplished by combining the factors of residual tumor mass (P less than .05), age (P less than .01), and clonogenic growth (P less than .05) (in sequence of decreasing potential of risk). 