To our knowledge, this is the first population-based study focusing on metastatic pancreatic cancer in patients initially diagnosed with CUP. This study examined patient characteristics associated with definitive diagnosis of metastatic pancreatic cancer in older patients who initially presented with CUP.
Definitive diagnosis of stage 3 or stage 4 pancreatic cancer in patients who initially presented with CUP was favorable in patients in the Other race category with fewer or no comorbidities. Unfavorable characteristics for definitive diagnosis included patients in older age groups and histology confirmed as epithelial/unspecified. Patients with comorbidities may receive health services more often than patients without comorbidities, thus are more likely to come in contact with the health care system [13]. However, older patients with comorbidities may be unable to complete the diagnostic workup necessary to make a definitive diagnosis [14]. Unfavorable characteristics for definitive diagnosis of CUP to a specified primary site including older age, epithelial/unspecified histology, and higher comorbid burden of disease correspond with current scientific literature on CUP patterns of care, namely population-based studies focusing on patient characteristics and healthcare utilization [3, 15–16], adherence and diagnostic guidelines [10], and risk factors and clinical management [17–18].
In patients diagnosed with stage 3 or stage 4 pancreatic cancer only, definitive diagnosis was similar to CUP patients by race, however, this subpopulation was younger and had fewer comorbidities overall. Furthermore, the comorbidity score and whether histology was epithelial/unspecified were not barriers to definitive diagnosis for the pancreatic cancer only group, suggesting there are imbalances in delivery of care compared to patients initially diagnosed with CUP. This is likely due to (a) the complexity of identifying the primary tumor site in CUP, whereas in identification of pancreatic cancer, the clinician at least has a point from which to begin a well-informed diagnostic process; and (b) poor performance status of the patient with CUP, a potential confounder this study could not account for.
These findings further elucidate the health disparities evident in CUP and pancreatic cancer diagnoses. Scientific literature on cancer health disparities report higher incidence of metastatic pancreatic cancer among Black and Latino patients, as well as lower occurrence of treatment (primarily surgical intervention), poor access to quality health care, and higher rates of overall morbidity and mortality [19–21]. An area of future research should focus on the patterns of care associated with race, ethnicity, and social determinants of health (to include socioeconomic status) in patients diagnosed with CUP and pancreatic cancer.
While SEER-Medicare data provided a robust sample size, there are limitations in this study. Furthermore, our study population was limited to patients 65 years and older and did not include patients with private insurance coverage. However, the age range of an average patient with CUP is 80 years or older and the vast majority of patients 65 years and older are insured through Medicare [22]. This study only investigated patients with a final metastatic pancreatic cancer diagnosis. Further research of other CUP-primary site cancers, for example ovarian and lung cancers, would be beneficial to the growing scientific literature on the diagnostic complexity of CUP. It is also important to note clinicians may need to report a definitive diagnosis to justify treatment for insurance claims. Claims data for administrative and billing purposes might be inaccurate from a biological or clinical disease perspective.