Background: Little data exist on patient perceptions of guideline-based care. This qualitative analysis describes patient and oncologist views on the value of discussing guidelines when making metastatic breast cancer (MBC) treatment decisions. Methods: In-person interviews completed by MBC patients and community medical oncologists and focus groups for academic medical oncologists were audio-recorded and transcribed. Two coders utilized a content analysis approach to analyze transcripts independently using NVivo. Major themes and exemplary quotes were extracted. Results: Participants included 20 MBC patients, 6 community oncologists, and 5 academic oncologists. The majority of patients (80%) were unfamiliar with the term “guidelines”. However, all patients desired to know if they were receiving guideline discordant treatment. As one patient commented “I'm supposed to know the guidelines and it's not supposed to be a secret to me.” Among patients willing to receive care inconsistent with guidelines, several themes emerged including trusting the oncologist, relying on the oncologist’s prior experiences, being informed of rationale for deviation, personalized treatment, and openness to novel therapies. Physician discussions on the importance of guidelines revealed themes such as consistency with scientific evidence, insurance coverage, and limiting unusual practices. Oncologists identified limitations to guidelines including lack of expert consensus, inability to “think outside the box” to personalize treatment, and lack of guideline timeliness. Although some oncologists discussed guidelines, a common sentiment was that sharing this information is not a priority. One physician commented that sharing the guidelines with patients is, “getting too much into the how you practice medicine, and they may not want to know, kind of like eating at a restaurant. You don't need to know how the cook's preparing everything.”Conclusions: Both patients and physicians expressed reasons why guideline discordant treatments would be acceptable. Providers’ preference to limit discussions of guidelines is discordant with patients’ desire for this information and may limit shared decision-making.