Background: The use of oral antineoplastic therapies has accelerated in recent years. Non-supervised administration of oncological therapies introduces uncertainty in regard to adherence. This review and meta-analysis reports on available literature relating to adherence, adherence-measuring methods, interventions to improve adherence, and estimates patient adherence to common oral antineoplastic therapies. Methods: A literature search was conducted in the PubMed database up to January 29, 2024 using relevant terminology for oral antineoplastic agents. Titles and abstracts of retrieved articles were screened, and full-text articles deemed of interest were reviewed. Studies suitable for meta-analysis and consistent with the analytical approach were selected based on adherence measurement methods and definitions. Random effects meta-analysis was conducted using the R package metafor and visualized with forest plots for cumulative adherence and lower-bound adherence separately. Results: We identified eight reviews and 75 original studies on adherence to non-endocrine oral antineoplastic agents, spanning the years from 1987 to 2023, with the vast majority published from 2010 onward. This review estimates the cumulative adherence to oral antineoplastic agents to be 84% (95% CI, 78–89) and lower-bound adherence as 71% (95% CI, 63–78). Conclusion: The definition of non-adherence and the measurement methods used across studies vary, rendering the comprehensive understanding of the subject challenging. This review identifies an adherence rate that deviates from full compliance across a wide variety of treatment regimens and tumor types, which could provide valuable insights for healthcare professionals in optimizing patient management.

Background: Antibody-drug conjugates (ADCs) are gaining rapidly expanding clinical utility, with a growing number of approved indications across compounds that differ in target antigen, payload mechanism, and linker design. However, treatment response remains heterogeneous, and predictive biomarkers to identify patients most likely to benefit are limited. Given that ADC efficacy depends on sufficient target antigen expression and distribution across tumor lesions, positron emission tomography (PET) imaging offers a unique opportunity to non-invasively assess whole-body target availability. We therefore conducted a systematic literature review to evaluate the relationship between PET-measured tumor antigen expression and the therapeutic response to ADCs targeting the same antigen. Method: A systematic comprehensive search of PubMed, EMBASE and Web of Science databases was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, using terms related to targeted PET, ADC treatment and response assessment. Article screening, eligibility assessment, and data extraction were performed independently using predefined criteria by two reviewers. Disagreements were resolved by consensus. Results: A total of 5628 records were identified. After removing duplicates, 4323 records were screened by title and Fifty-eight underwent full-text review and seven were included in the final review. Four trials investigated human epidermal growth factor receptor 2 (HER2)-targeted therapy, one Nectin-4, one mesothelin and one STEAP1. In all HER2- and Nectin-4-related trials, patients with a higher uptake on targeted PET had a higher probability of responding to targeted treatment. Included trials were generally small and had a moderate risk of bias. Conclusion: Targeted PET imaging showed potential to predict treatment response in trials evaluating clinically active agents. Additional clinical trials across a broader range of targets, along with standardized acquisition protocols and harmonized study designs, are needed to enable the integration of this technique into clinical practice and ultimately translate its benefits to patients.