Frequency of Bloodwork in Patients on Immune Checkpoint Inhibitors

Purpose: Immune checkpoint inhibitors (ICIs) are widely used to treat solid tumours. Prolonged use leads to increased bloodwork to monitor for adverse events (AEs). We explored the safety of decreasing bloodwork frequency while administering an ICI. Methods: Data was collected on patients receiving ICIs without chemotherapy for solid tumours from 2015 to 2020 at an academic cancer centre in Canada. Demographics, cancer diagnosis, ICI use, and pre-treatment bloodwork were extracted. The control group comprised all patients with all detected AEs. We modelled a decreased frequency of bloodwork by assuming that those same patients had bloodwork taken only every second or third cycle. The primary outcome was the proportion of patients with a missed bloodwork-related AE of grade 2 or higher. Descriptive statistics were used. Results: Among 735 patients, median age was 67, 65% were male, and most had lung cancer (39.6%) or melanoma (38.9%). Most (90.5%) received monotherapy. When neutropenia and lymphopenia were excluded, grade 2+ bloodwork-related AEs occurred in 20.9 to 27.7% of patients prior to cycle 2 of the ICI. When bloodwork is omitted every two or three cycles, respective AE miss rates were as high as 5.2 and 8.3% for thyroid abnormalities, 4.6 and 8.1% for hyperglycemia, and 1.6 and 2% for hepatitis. During the first period of bloodwork omission, overall grade 2+ AE miss rates were 10.4 to 12.4% when bloodwork was done every two cycles, and 17.9 to 23.8% when bloodwork was done every three cycles, varying by cycle duration. Miss rates were lower in later cycles. Conclusions: ICI bloodwork-related grade 2+ AE miss rates exceed 10% when bloodwork is omitted, suggesting that bloodwork should be obtained with each cycle of an ICI administered.