Factors associated with lower BDNF levels include a diagnosis of cancer (β = − 10.3, 95% CI − 13.7 to − 6.9, p < 0.001), female sex (β = − 2.8, 95% CI − 5.4 to − 0.1, p = 0.039), and time (in days) from baseline (β = − 0.018, 95% CI − 0.025 to − 0.010, p < 0.001). Here, BDNF is linked to cancer.