Syncope as a sign of occult cancers: a population-based cohort study.

We examined if syncope was a marker of an occult cancer by comparing the risk in patients with a syncope episode with that of the general population.Using Danish population-based medical registries, we identified all patients diagnosed with syncope during 1994-2013 and followed them until a cancer diagnosis, emigration, death or end of follow-up, whichever came first. We computed cumulative risks and standardised incidence ratios (SIR) with 95% confidence intervals (CI).Among 208,361 patients with syncope, 20,278 subsequent cancers were observed. The 6-month cumulative risk of any cancer was 1.2%, increasing to 17.9 % for 1-20 years of follow-up. The highest cumulative risks after 6 months of follow-up were lung cancer (0.2%), colorectal cancer (0.2%), prostate cancer (0.1%) and brain cancer (0.1%). The 6-month SIR were 2.7 (95% CI: 2.4-3.0) for lung cancer, 2.0 (95% CI: 1.8-2.2) for colorectal cancer, 1.7 (95% CI: 1.5-1.9) for prostate cancer and 10.0 (95% CI: 8.6-11.4) for brain cancer.Syncope was a weak marker of an occult cancer. In short-term the highest cumulative risks were observed for lung, colorectal, prostate and brain cancers. An aggressive search for occult cancer in a patient with syncope is probably not warranted.