Healthcare providers decide on recommendations for further treatment of patients with cancer in multidisciplinary tumor boards (MTBs). As such, communicative processes during MTBs are assumed to influence decision-making and, thereby, treatment planning. The aim of this exploratory study is to gain insights into decision-making during MTBs. Case discussions from MTBs in breast cancer centers in North Rhine-Westphalia, Germany, were observed and audiotaped. The transcripts of the audio recordings were analyzed by procedures of conversation analysis. Based on 38 case discussions from 15 MTBs in four breast cancer centers, an action scheme for decision-making in MTBs in breast cancer care was developed. In addition, the conversational practices used by the participants during interactions were analyzed. Analysis indicated that conventions in MTBs were observed during individual phases of decision-making but not for the entire process. Although exchanging multidisciplinary knowledge is an essential aspect of MTBs, this exchange does not always seem to occur in practice. The extent to which recommendations are derived from consensus during MTBs remains unclear. Thus, the study suggests developing standards for communication during MTBs to optimize decision-making and, thus, the quality of recommendation.