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Research Article
21 October 2026

Real-world utilization of pembrolizumab dosing schedules in Belgium: a multi-center retrospective study using a common data model and natural language processing

Authors: Annelies Verbiest https://orcid.org/0000-0001-9024-863X [email protected], Hans Prenen https://orcid.org/0000-0001-8802-7352, Annelies Janssens https://orcid.org/0000-0002-1464-163X, Christof Vulsteke https://orcid.org/0000-0002-4607-5660, Danielle Delombaerde https://orcid.org/0000-0003-1660-6237, Laura Tack https://orcid.org/0000-0002-0623-0160, Philip R Debruyne https://orcid.org/0000-0001-5438-9697, … Show All … , Iege Bassez https://orcid.org/0000-0001-8931-0029, Clara L Oeste https://orcid.org/0000-0002-7035-132X, Agnes Brandtmüller https://orcid.org/0009-0007-8351-6801, Carl Baxter, Pieterjan Debie https://orcid.org/0000-0002-9128-7814, and Jan Vertriest https://orcid.org/0009-0001-6744-2917Author Info & Affiliations
Volume 15, Number 11
https://doi.org/10.57264/cer-2026-0011
PDFFormats

Abstract

Aim: Pembrolizumab's six-week extended dosing (ED), approved as an alternative to the standard three-week schedule (SD), offers flexibility in treatment plans. Materials & methods: In this retrospective study across four Belgian hospitals, we described real-world pembrolizumab utilization using a pipeline that processed unstructured data with natural language processing (NLP) and mapped both structured and unstructured data to an OMOP-CDM database. Physicians and data analysts collaboratively developed the project-specific data dictionary and performed validation. Results: A total of 303 patients were included, 56% with non-small cell lung cancer (NSCLC). Most patients (72%) received monotherapy, with 89% starting on SD. For NSCLC first-line monotherapy, the median time on treatment (rwTOT) was 106 days in the ‘SD only’ cohort and 666 days in the ‘SD to ED’ cohort, while the median time to next treatment (rwTTNT) was 280 days for ‘SD only’ (median rwTTNT not reached for ‘SD to ED’). Dosing cohort distributions showed that 74% of patients in the ‘SD to ED’ group had NSCLC, compared with 77% with urothelial cancer in the ‘ED only’ group. The mean (StdDev) gap between administrations was 23 (7) days for SD and 43 (5) days for ED. Most patients receiving ED did so after starting on SD, and all ED initiators stayed on ED. Dosing patterns remained stable pre- and during COVID-19. Conclusion: This study describes real-world pembrolizumab dosing patterns across four Belgian hospitals and illustrates how integrating NLP and structured data within an OMOP-CDM framework can support such analyses. Patients switching from SD to ED showed longer rwTOT and rwTTNT than those on SD alone, though potential immortal time bias requires caution in interpretation.

Plain language summary: How pembrolizumab dosing schedules are used in Belgian hospitals using routine health data

What is this article about?

Pembrolizumab is a cancer treatment that can be given every 3 weeks (standard dosing) or every 6 weeks (extended dosing). The extended schedule may reduce hospital visits and improve convenience for patients. However, there is limited information on how these schedules are used in routine care.
In this study, we used routinely collected data from four Belgian hospitals, including information from both structured records and clinical notes, to describe how pembrolizumab is used in practice. This study also shows how advanced data methods can help answer clinical questions using real-world data.

What were the results?

We included 303 patients receiving pembrolizumab. Most patients started on the standard schedule, and many stayed on it. Among those who received extended dosing, most switched from the standard schedule after some time. Patients who switched to extended dosing tended to remain on treatment longer. However, this reflects how the groups are defined and should be interpreted with caution. Dosing patterns remained stable over time, including during the COVID-19 pandemic.

Why is this important?

This study shows that real-world hospital data can be used to understand how cancer treatments are used in practice. The findings suggest that extended dosing is feasible and may reduce the number of hospital visits. However, differences between dosing groups do not necessarily reflect differences in treatment effectiveness.

Supplementary Material

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