Introduction Antimicrobial resistance (AMR) is a growing global public health concern and is becoming a significant challenge in the management of patients with cancer. Due to the immunosuppressive nature of cancer treatment, infection is a common complication and the necessary high usage of antibiotics increases the risk of AMR. Failure to adequately prevent and treat infection in patients with cancer as a result of AMR can increase the morbidity and mortality of the disease. The objective of this scoping review is to understand the relationship between AMR and cancer in order to develop effective antimicrobial stewardship in this patient population and minimise the detrimental effects of AMR on cancer outcomes. Methods and analysis This scoping review will follow the Arksey and O’Malley methodology framework. An exploratory review of the literature on antibiotic resistance in cancer care will help to define the research questions (stage 1). A broad range of electronic databases (MEDLINE ALL, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews and Embase) and search terms will be used to retrieve relevant articles published between 2000 and 2021 (stage 2). Studies will be systematically selected based on the eligibility criteria by two independent reviewers (stage 3). The titles and abstracts will be appraised to determine whether articles meet the eligibility criteria. This will be followed by screening of the full texts and only relevant publications will be retrieved. Data will then be extracted, collated and charted (stage 4); and the summary of aggregated results will be presented (stage 5). Ethics and dissemination As this scoping review will collect and synthesise data from publicly available sources, no ethics review is required. When data collection and summarisation is completed, results will be disseminated through peer-reviewed publication and the key findings of the review will be presented at relevant conferences.

Ductal carcinoma in situ (DCIS), especially in the era of mammographic screening, is a commonly diagnosed breast tumor. Despite the low breast cancer mortality risk, management with breast conserving surgery (BCS) and radiotherapy (RT) is the prevailing treatment approach in order to reduce the risk of local recurrence (LR), including invasive LR, which carries a subsequent risk of breast cancer mortality. However, reliable and accurate individual risk prediction remains elusive and RT continues to be standardly recommended for most women with DCIS. Three molecular biomarkers have been studied to better estimate LR risk after BCS—Oncotype DX DCIS score, DCISionRT Decision Score and its associated Residual Risk subtypes, and Oncotype 21-gene Recurrence Score. All these molecular biomarkers represent important efforts towards improving predicted risk of LR after BCS. To prove clinical utility, these biomarkers require careful predictive modeling with calibration and external validation, and evidence of benefit to patients; on this front, further research is needed. Most trials do not incorporate molecular biomarkers in evaluating de-escalation of therapy for DCIS; however, one—the Prospective Evaluation of Breast-Conserving Surgery Alone in Low-Risk DCIS (ELISA) trial—incorporates the Oncotype DX DCIS score in defining a low-risk population and is an important next step in this line of research.