Monoclonal antibodies targeting PD-1 are used for treating NSCLC. To date, proprotein convertase subtilisin/kexin type 9 (PCSK9) has been poorly investigated in the oncologic field. Here, we aimed at evaluating whether serum PCSK9 might represent a predictive factor for OS in older patients with advanced NSCLC under nivolumab treatment. Among 78 patients with advanced, pre-treated NSCLC previously enrolled in a prospective study at Ospedale Policlinico San Martino in Genoa (Italy), 44 patients have been included in this sub-analysis due to the availability of serum samples for the measurement of PCSK9. Before each nivolumab administration, clinical information and blood samples were collected. Median age was 71, with a prevalence of the male sex. The most represented histological type of lung cancer was adenocarcinoma. The majority of patients were former smokers (72.1%). Median PCSK9 levels were 123.59 (86.32-169.89) ng/mL and 117.17 (80.46-147.79) ng/mL at cycle 1 and 2, respectively. Based on a receiver operating characteristic curve analysis, a PCSK9 value at cycle 2 of 95 ng/mL was found as the best cutoff point for OS. Kaplan-Meier analysis demonstrated that patients below the PCSK9 cutoff (< 95 ng/mL) experienced a better OS, as confirmed by Cox proportional hazard regression analysis. In this pilot study, circulating levels of PCSK9 < 95 ng/mL at the time of the second cycle of nivolumab treatment could independently predict a better OS in elderly patients with advanced, pre-treated NSCLC. However, further studies are warranted to validate these preliminary results.