Jaana Oikkonen

Background: Antibody-drug conjugates (ADCs) represent a promising precision medicine approach for difficult-to-treat cancers, yet the spatial, temporal, and cellular heterogeneity of clinically approved ADC targets in ovarian high-grade serous carcinoma (HGSC) remains incompletely defined. Methods: We analyzed bulk RNA-sequencing, single-cell RNA-sequencing, and whole-genome sequencing data from 867 samples across 304 patients enrolled in the real-world, observational DECIDER cohort to systematically evaluate 11 approved ADC targets. Results: Here we show that FOLR1 , TACSTD2 , and ERBB2 emerged as highly expressed candidates. Inter-patient variability exceeded intra-patient heterogeneity, which further decreased after neoadjuvant chemotherapy. Target expression was highly concordant across anatomical sites and largely stable from diagnosis to relapse. Single-cell RNA-sequencing results revealed that TACSTD2 and FOLR1 showed the most frequent cancer cell-restricted expression. In rare cases of gene amplification, ERBB2 and F3 emerged as potential targets alongside TACSTD2 and FOLR1 . Overall, 80% of patients displayed homogeneous expression of at least one actionable target, with frequent co-expression of TACSTD2 and FOLR1 . Conclusions: These findings indicate that ADC target expression in HGSC is broadly stable across space and time and support the prioritization and strategic integration of TACSTD2 - and FOLR1 -directed ADCs.

Identification and functional validation of inactivating mutation on a source RC-L1

Catalog and Characteristics of L1 insertions identified by LDI-PCR/Nanopore-seq

Association of L1 status of HGSC patients with their genomic features

Primers and reaction conditions for Genotyping PCR

Agarose gel image showcasing results of source RC-L1s genotyping PCR

Within-patient variability in L1 profiles

PCR validation of de novo L1 insertions identified by LDI-PCR/Nanopore-seq

Agarose gel image showcasing results of Long-distance Inverse PCR (LDI-PCR) to detect de novo L1 retrotransposition in HGSC tumors