Barriers to study enrollment in patients with advanced cancer referred to a phase I clinical trials unit.

UNLABELLED: We conducted this retrospective study to identify reasons that patients referred to a phase I clinical trial failed to enroll or delayed enrollment onto the trial. MATERIALS AND METHODS: Outcome analyses were conducted independently on data collected from electronic medical records of two sets of consecutive patients referred to a phase I clinical trial facility at MD Anderson Cancer Center. Data from the first set of 300 patients were used to determine relevant variables affecting enrollment; data from the second set of 957 patients were then analyzed for these variables. RESULTS: Results from the two sets of patients were similar. Approximately 55% of patients were enrolled in a phase I trial. Patients referred from within MD Anderson were more likely to be enrolled than patients seen originally outside the institution (p = .006); black patients were more likely than white patients to enroll (69% vs. 43%; p = .04). The median interval from the initial visit to initiation of treatments was 19 days. Major reasons for failure to enroll included failure to return to the clinic (36%), opting for treatment in another clinic (17%), hospice referral (11%), early death (10%), and lack of financial clearance (5%). Treatment was delayed for three weeks or more in 250 patients; in 85 patients (34%), the delay was caused by financial and insurance issues. CONCLUSION: Failure to return to the clinic, pursuit of other therapy, and rapid deterioration were the major reasons for failure to enroll; lengthy financial clearance was the most common reason for delayed enrollment onto a phase I trial.

Noise reduction by diffusional dissipation in a minimal quorum sensing motif.

Cellular interactions are subject to random fluctuations (noise) in quantities of interacting molecules. Noise presents a major challenge for the robust function of natural and engineered cellular networks. Past studies have analyzed how noise is regulated at the intracellular level. Cell-cell communication, however, may provide a complementary strategy to achieve robust gene expression by enabling the coupling of a cell with its environment and other cells. To gain insight into this issue, we have examined noise regulation by quorum sensing (QS), a mechanism by which many bacteria communicate through production and sensing of small diffusible signals. Using a stochastic model, we analyze a minimal QS motif in Gram-negative bacteria. Our analysis shows that diffusion of the QS signal, together with fast turnover of its transcriptional regulator, attenuates low-frequency components of extrinsic noise. We term this unique mechanism "diffusional dissipation" to emphasize the importance of fast signal turnover (or dissipation) by diffusion. We further show that this noise attenuation is a property of a more generic regulatory motif, of which QS is an implementation. Our results suggest that, in a QS system, an unstable transcriptional regulator may be favored for regulating expression of costly proteins that generate public goods.