Inclusion in the cancer patient pathway among cancer patients with and without pre-existing mental or substance use disorders: a nationwide register-based study

Abstract Background Cancer patients with a pre-existing mental disorder or substance use disorder (SUD) have a poorer prognosis compared to other cancer patients, with suboptimal routes to diagnosis and treatment as possible contributing factors. Shorter intervals from suspicion of cancer to start of cancer treatment have been observed following the implementation of Cancer Patient Pathways (CPP) in the Nordic countries, which may have led to a better prognosis. We aimed to investigate whether incident cancer patients with and without pre-existing mental disorder or SUD were equally likely to be included in a CPP. We also investigated the associations between pre-existing mental disorder or SUD and low primary care utilization, and cancers diagnosed post-emergency or close to death in non-CPP enrolees. Methods This population-based registry study included incident cancer patients aged 21–79 between 2015 and 2018 (n = 65,328). Information on pre-existing mental disorders or SUD was gathered from national registries of primary and specialised health care, prescriptions, and disability diagnosis. Propensity score analyses using inverse probability weighting along with the McNemar test were performed to evaluate the risk of non-inclusion in any CPP for all cancers combined, lifestyle-related cancers combined, and the most common cancers individually. Results Cancer patients with pre-existing mental disorder or SUD had an 8% (RR = 1.08; 95% Confidence Interval (CI) 1.03–1.13) higher risk of non-enrolment in a CPP. Patients with prior hospitalisation for mental disorder or SUD, and patients with pre-existing psychosis or depression were at particular risk of non-inclusion in a CPP compared to controls, especially for cancers that often present with symptoms late in the course of the disease, such as lung cancer. In line with this, patients with pre-existing mental disorder or SUD who were not referred to a CPP faced a 34% (RR = 1.34; 95% CI 1.18–1.53%) increased risk of unrecognised cancer close to death. Conclusions Cancer patients with pre-existing mental disorder or SUD have an increased risk of non-inclusion in a CPP. If not included in a CPP, they have an increased risk of having unrecognised cancer close to death. By addressing barriers to CPP-inclusion, and enhancing the quality of diagnostic and treatment services, healthcare systems could achieve better cancer outcomes for vulnerable patient groups.