Dyspnea is an extremely distressing symptom (Dudgeon et al., 2001) that has a negative impact on oncology patients' quality of life (QOL) and in some cases is associated with decreases in survival (Lou et al., 2017). Despite its tremendous burden, dyspnea is often underestimated by clinicians (Meriggi, 2018). For example, while clinicians reported that less than 30% of patients with lung cancer experienced moderate to severe dyspnea, over 50% of their patients reported the occurrence of this symptom (Iyer et al., 2014).

One possible explanation for this discrepancy between patients’ and clinicians’ appraisals of dyspnea is the large amount of inter-individual variability in its occurrence across various types of cancer. In patients with lung cancer (Iyer et al., 2014, Kim et al., 2016, Weingaertner et al., 2014) or advanced cancer (Bausewein et al., 2010b, Ekström et al., 2016, Reddy et al., 2009), the prevalence rates for dyspnea range from 10% to 90%. Factors that contribute to this variability include: gender, cancer types, presence of metastatic disease, receipt of previous cancer treatment(s), smoking history, environmental factors, comorbidities (Dudgeon et al., 2001), and/or presence of co-occurring symptoms (Reddy et al., 2009). However, exact prevalence rates and associated risk factors in patients with other types of cancer warrant additional investigation.

While guidelines published by the American Thoracic Society (ATS) (Parshall et al., 2012), the National Comprehensive Cancer Network (NCCN) (Dans et al., 2021), and the American Society of Clinical Oncology (ASCO) (Hui et al., 2021c), all use the term “dyspnea”, the definition of this symptom, as well as the terms that should be used to assess its occurrence, severity, distress, and impact are not standardized (Booth et al., 2008). Of note, patients use a variety of words to describe dyspnea (e.g., "shortness of breath", "difficulty breathing", "chest tightness", “air hunger" (Booth et al., 2008; Chowienczyk et al., 2016; Parshall et al., 2012; Reddy et al., 2009)). This lack of a standardized nomenclature is a significant limitation to be able to make comparisons across studies (Miaskowski, 2016) and develop a comprehensive symptom assessment instrument.

Dyspnea is a multidimensional symptom that warrants evaluation using the domains of sensory-perceptual experience, affective distress, and impact (Parshall et al., 2012). While a number of measures are used routinely in dyspnea research (e.g., Medical Research Council (MRC) Dyspnea scale (Boşnak Güçlü et al., 2021, Greer et al., 2015, Murray et al., 2016, Suzuki et al., 2019), Modified Borg scale (Dewi Puspawati et al., 2017, Minchom et al., 2016, Stefanelli et al., 2013), numeric rating scale (NRS) (Navigante et al., 2010; Simon et al., 2016; Yamaguchi et al., 2018)), most of them do not assess the multiple dimensions of patient’s experience with dyspnea (Parshall et al., 2012). In addition, because most of the dyspnea measures were developed before the ATS published their consensus definition (Parshall et al., 2012), very few measures have included an assessment of the affective dimension of dyspnea (Banzett et al., 2015, Eakin et al., 1998, Hollen et al., 1993, Tan et al., 2017, Tanaka et al., 2000).

Taken together, no consensus exists on the specific instruments to use to assess the occurrence, severity, distress, and/or impact of dyspnea in oncology patients. To date, the only systematic review of dyspnea in oncology patients focused solely on patients with lung cancer (Kathiresan et al., 2010). This limitation is a significant one because in a cross-sectional study of dyspnea in 923 oncology patients (Dudgeon et al., 2001), only 9.4% had primary and metastatic lung cancer. The remaining 90.6% of patients with heterogeneous types of cancer experienced dyspnea from a variety of factors (e.g., cancer treatment(s), comorbid conditions). Given the paucity of research on the prevalence, severity, distress, and impact of dyspnea in oncology patients, this systematic review was undertaken to answer the following questions: 1) What are the most common terms used to assess for dyspnea?; 2) What are the most common instruments used to assess for dyspnea?; 3) What are the most common dimensions of the symptom experience that are used to describe dyspnea?; 4) What are the most common risk factors for dyspnea?; 5) What are the most common outcomes that are evaluated in studies that assess dyspnea?; 6) What are the most common co-occurring symptoms associated with dyspnea?; 7) What is the relationship between stress and dyspnea?, and 8) What are the most common biomarkers associated with dyspnea?