Reflectance confocal microscopy and pathological correlation of tumor microenvironment in adnexal cancers during balstilimab treatment

Abstract

Adnexal carcinomas (AC) are rare, locally aggressive tumors with limited systemic treatment evidence and no validated immunotherapy biomarkers. Reflectance confocal microscopy (RCM) enables non-invasive, in vivo tumor microenvironment (TME) imaging at near-histologic resolution. We report the first prospective topographical correlation of RCM with videodermoscopy, histopathology, and immunohistochemistry (IHC) in advanced AC patients treated with balstilimab (anti-PD-1) in the AGENONMELA phase II study (EUDRACT 2020-004622-29, ABM_01_00004_03). Patients with unresectable or metastatic AC underwent longitudinal RCM and videodermoscopy imaging at screening, week 12, and end-of-treatment, with two RCM-guided biopsies per lesion. RCM immune cell patterns, vascularity, and stromal architecture were correlated with H&E and IHC (CD4, CD8, CD1a, CD68, CD209, FOXP3) via blinded central review. RCM-IHC topographical correlation was feasible in five patients. RCM identified spatially heterogeneous tumor-infiltrating lymphocytes, stromal remodeling, necrotic structures, and vascularity with high IHC concordance. Dynamic immune features preceded radiologic progression in non-responders. All patients except one (sebaceous carcinoma, Muir-Torre syndrome) demonstrated primary resistance to PD-1 blockade. RCM provides real-time, non-invasive TME characterization in advanced AC, enabling immune architecture monitoring beyond conventional histology. This RCM-IHC topographical correlation supports RCM as a translational biomarker tool in AC. Limitations included a small sample size, a heterogeneous histologic spectrum of adnexal carcinomas, technical penetration limit of RCM. RCM-to-IHC correlation was topographic and qualitative/semi-quantitative rather than based on exact cell-by-cell registration.