Background: Patients and clinicians do not often agree on whether a decision has been made about cancer care. This could be explained by factors related to communication quality and/or the type of decision being made. Methods: We used a self-developed coding scheme to code a random sample of 128 encounters in which patients and clinicians either agreed (n=64) or disagreed (n=64) that a cancer care decision was made and tested for associations between concordance and key communication behaviours. We also identified and characterized cancer care decisions by topic and level of patient involvement and looked for trends. Results: We identified 378 cancer care decisions across 128 encounters. Explicit decisions were most commonly made about topics wherein decision control could be easily delegated to a clear and present expert (eg either the patient or the clinician). Related to this, level of patient involvement varied significantly by decision topic. Explicit decisions were rarely made in an observable way about social, non-clinical or self-management related topics, although patients and clinicians both reported having made a cancer care decision in encounters where no decisions were observed. We found no association between communication behaviours and concordance in our sample. Conclusions: What counts as a “decision” in cancer care may be constructed within disparate social roles that leave many agendas unaddressed and decisions unmade. Changing the content of conversations to encourage explicit decisions about self-management and life context-related topics may have greater value in enabling shared understanding than promoting communication behaviours among already high-performing communicators.