The presence of one or more additional diseases (comorbidity) does not affect the risk of dying from prostate cancer, regardless of treatment type, a Swedish observational study reports. However, high comorbidity in prostate cancer patients is linked with increased mortality from other causes.

The study, “Effect of Comorbidity on Prostate Cancer–Specific Mortality: A Prospective Observational Study,” was published in The Journal of Clinical Oncology.

“Comorbidities are medical disorders that coexist with, but are distinct from, the primary diagnosis,” authors explained. They are usually associated with worsening health outcomes.

While researchers have addressed comorbidity in prostate cancer patients, studies have reported conflicting results on its association with prostate cancer mortality.

Researchers at the Queen Mary University of London, England, and the Karolinska Institute in Stockholm, Sweden, and colleagues investigated the effect of comorbidities on prostate cancer-specific mortality after accounting for patient and tumor characteristics.

Treatment type was also taken into account in their analysis. These included radical prostatectomy (a surgical procedure for removing the prostate gland); radical radiotherapy (a non-surgical treatment using radiation); androgen deprivation therapy, and watchful waiting (a strategy that monitors prostate cancer that isn’t causing any symptoms and avoids treatment unless it becomes symptomatic).

The study included 118,543 prostate cancer patients from the Prostate Cancer Database in Sweden from 1998 to 2012. Patients were followed for a median of 8.3 years until they died, either from prostate cancer or from other causes. Comorbidity registers were retrieved from 10 years before, until the date of prostate cancer diagnosis.

An initial analysis that did not account for either patient and tumor characteristics or treatment type showed that comorbidities affected the risk of patients dying specifically due to prostate cancer and from other causes. Patients with the highest comorbidity score were two times more likely to die from prostate cancer, and five times more likely to die from any other cause.

But after accounting for patient (marital status, educational level) and tumor characteristics (PSA levels, tumor grade, and clinical stage) the team failed to detect any effect of comorbidity on prostate-cancer specific mortality. The effect was maintained, however, for mortality due to other causes.

The same lack of effect was observed when they further adjusted for each treatment type. The association to other-causes mortality remained unaltered, with the most striking effect observed in patients treated with radical prostatectomy. Patients with high comorbidity had a 4.42-fold increase in mortality from other causes, compared to those without comorbidities.

Overall, these results suggest “that comorbidity affects other-cause mortality but not prostate cancer-specific mortality, accounting for patient and tumor characteristics and treatment type,” the study concluded.