Due to the increasing incidence of cancer and advancements in its detection and treatment, the number of people living with cancer as a chronic condition is increasing [1,2]. With improved survival comes new challenges, as secondary health problems and symptoms related to cancer and treatment can persist for years following diagnosis [3]. Adverse effects including functional and cognitive impairments, physical symptoms, risk of secondary cancers, comorbidities, and poor psychosocial outcomes can have debilitating and lifelong consequences for cancer survivors and their families [3]. Accordingly, the definition of treatment efficacy has moved beyond survival alone, and there is a greater emphasis on establishing the impact of treatments on quality of life [4]. Increasing efforts to quantify the subjective experience of illness, treatment, and side effects using patient-reported outcomes (PROs) have led to a proliferation in the number of patient-reported outcome measures (PROMs) available to assess aspects of health, functioning, and quality of life from the patient's perspective [4].

The potential uses of PRO data can be understood using the Lipscomb framework for cancer outcomes research, which proposes three arenas for the application of PROs: micro, meso, and macro [5]. At the micro or individual level, PRO data are used to support and enhance patient-centered care, patient-clinician interactions, and decision making in clinical settings [4]. At the meso or service level, PRO data are used to understand the variables that influence health outcomes. PRO data collected at a macro level can be used to monitor and understand trends in health outcomes across a population [5]. Although there are few established systems internationally for the routine collection of macro-level PRO data (known as PRO surveillance), there is increasing recognition that expanding and optimizing the role of cancer registries to include PRO surveillance would improve our understanding of the long-term trajectory of survivorship outcomes on a national scale [6].

A challenge in PRO research is the lack of standardization and comparability of scores from different PROMs. For any given outcome, there may be multiple measures developed for different purposes, populations, and disciplines. Core outcome sets have been proposed as a way of addressing these problems. A core outcome set is a recommended, standardized, and minimum set of outcomes to be measured and reported in research on a specific health condition and which should be agreed upon by relevant stakeholders [7,8]. By standardizing the outcomes that are examined across studies, use of core outcome sets can help minimize bias in outcome selection and reporting and facilitate data comparison and synthesis [9]. Core outcome sets have been developed for various diseases including cancer, but not for the assessment of long-term cancer survivorship concerns at a population level. Predominantly tumor-specific core outcome sets with a typically acute focus have been developed to facilitate standardized assessment of treatment-related symptoms and toxicities in clinical trials.

This study aims to develop a core outcome set, recommending what PROs should be collected as a minimum for surveillance of cancer survivorship concerns in Australia and how these outcomes should be measured. The need for a set of outcomes applicable to all cancers is underscored by research identifying issues common across cancer sites in the long-term [10] including psychosocial outcomes, fatigue, functional impairment, fear of recurrence, and limitations in health care and insurance access [11]. The core outcome set will be developed using recommended methods, including a Delphi consensus process. The Delphi technique is a well-recognized method for obtaining expert consensus on a defined problem [12] and is used frequently in health research and core outcome set development.

As of April 2019, data collection for Phase I is complete and data analysis is underway. These data will inform the list of outcomes to be progressed into Phase II. Recruitment for Phase II will commence in June 2019, and it is anticipated that it will take 6 months to complete the three-step consensus process and identify a provisional core outcome set. The study results are expected to be published in early 2020.

Problems arising from the heterogeneity of PROMs have been documented in cancer survivorship research [28] and other areas of health research [15]. A review of registries that systematically collect PRO for population-level surveillance of cancer survivorship outcomes recommended that consensus be obtained on a core set of outcome domains and measures to improve the consistency and comparability of data collected [28]. Adoption of the proposed core outcome set by researchers could enhance the quality of future research by helping ensure the inclusion of relevant survivorship outcomes that are important to consumers and the use of validated tools that are sensitive to survivorship. In addition to macro-level application, the proposed core outcome set could also guide researchers seeking to use survivorship PROMs in clinical trials or extended follow-up beyond acute settings. To maintain relevance, the core outcome set may need to be periodically checked and updated to reflect consequences of new treatment modalities.

This is not the first core set of outcomes to be developed for all cancers, although it is unique in its scope and intended end use. In 2011, the National Cancer Institute’s Symptom Management and Health-Related Quality of Life Steering Committee led an international effort to identify a core set of patient-reported symptoms to be measured in all adult cancer treatment trials [10] as well as disease-specific core symptom sets for head and neck, prostate, and ovarian cancers [29-31] to be used in conjunction with the generic cancer set. Since self-reported symptoms offer important insight into intervention efficacy and toxicities, increased consistency of symptom assessment across trials using the patient-reported core symptom sets may help improve care quality for clinical trial participants [10]. Our study aims to promote consistent assessment across the growing number of systems collecting PRO data from cancer survivors at a population level. Therefore, agreement on a core set of PROs similar to the set developed by the National Cancer Institute but (1) representing the health, functioning, and quality of life issues that are important in long-term cancer survivorship (ie, not exclusive to disease and treatment-related symptoms) and (2) suitable for the purpose of macro-level surveillance (ie, not specific to clinical trials) is warranted [10,28]. Despite a shared aim of facilitating consistent assessment of PROs in research with cancer populations [10], the core outcome set developed by the National Cancer Institute will inform assessment of disease- and treatment-related symptoms in clinical trials, while the proposed core outcome set for cancer survivorship will play a complementary role in informing population-based surveillance of quality of life among cancer survivors beyond clinical settings.

In the Netherlands, Geerse et al [32] developed a core set of International Classification of Functioning, Disability, and Health (ICF) categories for health-related problems in adult cancer survivors. In addition to being based on the ICF, their Cancer Survivor Core Set differs from the proposed core outcome set in intended purpose and development methods. Three panels of 25 survivorship experts for colorectal, breast, and lung cancers participated in a two-round Delphi study where 265 ICF categories were used for item selection [32]. The resulting core outcome set included 19 items, 11 of which were linked to corresponding item(s) on at least one of three selected cancer survivorship PROMs. The intended application of the core outcome set developed by Geerse et al [32] is not specified, although the authors state that it could be used as a screening tool. In contrast, the proposed core outcome set is intended to reflect the most important and relevant survivorship issues beyond acute symptoms that should be collected in routine PRO surveillance in Australia. Item selection will be informed by existing PROMs and oncological PRO frameworks rather than the ICF. Adults of different ages with a diverse range of cancers will be represented in the development process. It will be beneficial to understand the similarities and differences in outcomes prioritized by the current Australian-led research and the core outcome set developed in the Netherlands.

We based the study methods on recommendations for evidence-based core outcome set development [23], guidelines for using the Delphi technique to obtain consensus on core outcomes [27], standards for core outcome set study design [33], and previous core outcome set studies with cancer populations that employed Delphi methods [26,34]. However, there is no agreed-upon methodology for developing a core outcome set. It is therefore unclear to what extent the results from this study would be concordant with those obtained in different settings, using alternate consensus methods, or applying different criteria. Despite these limitations, the study design is considered suitable for the scope and setting of this core outcome set and will allow a large and geographically diverse sample of stakeholders to participate.

Although there is little scientific evidence regarding the optimal number of Delphi rounds, two or three rounds have been frequently recommended [35] and commonly used in core outcome set development studies [23]. Given that we will undertake a rigorous process to identify, select, and refine the initial outcome list to be progressed into the Delphi and include a face-to-face meeting to agree on the final core outcomes, two survey rounds were considered sufficient. An advantage of restricting the number of rounds is that this can limit potential bias due to attrition, which is likely to increase with each round. A limitation of restricting the study to two survey rounds is that it may not be possible to confirm stability of voting, although this is generally thought to be a measure of internal reliability and not consensus. Instead, we will be measuring the extent to which participants agree with the statements under consideration (agreement) and the extent to which participants agree with each other (consensus) [36]. It is not possible to determine the validity of any specific definition of consensus in Delphi studies, but the proportion of ratings within a range is one of the most commonly employed consensus definitions and the median is considered the most robust measure of central tendency [36].

Another potential limitation is that we are conducting a review of cancer survivorship PROMs rather than of all outcomes that have been examined in cancer survivorship research, and therefore, we may not identify all possible relevant outcomes. This risk will be mitigated by additionally identifying outcomes in Phase I from focus groups with cancer survivors and providing Delphi participants with the opportunity to suggest additional outcomes in Phase II.

This protocol describes the development methods for a core set of PROs to inform our understanding of the long-term impacts of cancer on survivors’ quality of life at a population level. Since the proposed set represents the minimum outcomes that should be collected and reported on, it can be supplemented with other outcomes or measures relevant to a given study setting or population. By providing consensus-driven recommendations from stakeholders with expertise in cancer survivorship research, practice, policy, and lived experience, the study findings will facilitate the inclusion of meaningful survivorship outcomes and enhance the quality and comparability of PRO data collected in survivorship research, particularly when applied to address macro-level questions.