Objective: To study the relationship between cancer patient/research participants' perceptions of communication with their research nurse and doctor and (1) participants’ thoughts of dropping out from their cancer clinical trials (CCTs), (2) how informed they felt before and during their clinical trial participation, and (3) trust in their researchers. Methods: We surveyed 110 adult cancer patients who were enrolled in cancer clinical trials by using 15 modified items from the Medical Communication Competence Scale measuring information exchange and relational communication. Retention was measured by two items: ever thought about dropping out (yes/no) and likelihood of remaining enrolled in the clinical trial (5-point Likert item). We asked how well informed about the trial participants felt at enrollment, at the date they filled out the survey, and about changes in the trial. Results: Patient-participants with thoughts of dropping out from their CCTs rated their communication with research doctors lower than those who did not have thoughts of dropping out (4.14 versus 4.46, t = 2.22, p = 0.03). Patient-participants' intention to remain enrolled was correlated with more favorable scores on relational communication (such as contributing to a trusting relationship and showing compassion) with research doctors (r = 0.20, p = 0.04) and nurses (r = 0.25, p = 0.01). Communication with doctors was also associated with how informed patient-participants felt during their clinical trials. Conclusions: Relational communication with research doctors and nurses was significantly related to thoughts about remaining enrolled or dropping out of a clinical trial among adult participants in cancer treatment clinical trials. Practice Implications: Relational communication with cancer patients advances retention in research.