Standard: human breast cancer organoids derived from diverse clinical sample sources.

Breast cancer remains a leading cause of cancer-related morbidity and mortality worldwide, driven by therapeutic resistance, recurrence, and metastasis. Patient-derived organoids (PDOs) have emerged as a robust platform that preserves histopathological, genetic, and functional features of parental tumors, enabling translational research and precision oncology. However, the lack of standardized procedures across laboratories limits reproducibility and clinical applicability. Here, we present a consensus-oriented standard for the establishment, characterization, quality control and application of human breast cancer organoids derived from diverse clinical sources, including surgical tissues, biopsies, pleural effusion, ascites, and circulating tumor cells (CTCs). This document defines key terminologies, outlines standardized workflows, and introduces quantitative validation criteria for successful organoid establishment. In addition, it provides structured guidance for advanced models, including immune-tumor, neuro-tumor, and microbiota-tumor organoid systems, with defined functional validation endpoints. Standardized protocols for drug sensitivity testing are also proposed, including seeding density, exposure duration, and response metrics such as IC50 and AUC. Representative validation strategies, including histological, molecular and functional concordance with parental tumors, are incorporated to enhance reproducibility and translational relevance. This standard aims to harmonize methodologies, improve cross-study comparability, and accelerate the clinical implementation of breast cancer organoid-based precision medicine.