A joint project of the International Academy of Cytology (IAC), the International Academy for Research into Cancer (IARC) and the World Health Organisation (WHO) has developed eight reporting systems in cytopathology with the WHO Reporting Systems in Lung, Pancreaticobiliary, Lymph node, Thymus and Spleen, and Soft Tissue published between 2022 and 2025, and four further Systems in Breast, Liver, Kidney and Adrenal, and Head and Neck nearing completion. The systems are designed to improve communication between cytopathologists and clinicians by integrating clinical and imaging context with a diagnostic category, cytopathological criteria and ancillary testing. The internationally standardized categories are linked to a hierarchial risk of malignancy, and practical diagnostic management recommendations for cytopathology specimens across organ systems. Key diagnostic cytopathological features for entities have been developed through consensus by the expert editorial boards with global representation, and the Systems emphasize the importance of specific diagnoses and differential diagnoses based on these features. In addition, detailed standardized information is provided on the use whenever available of ancillary testing including pre-analytical handling and preparation of specimens. Practical information on the role of cytopathology and on specimen procurement is provided. The new reporting systems have generated research on their usefulness and accuracy leading to a beneficial focus on cytopathology in various medical resource settings. The development process has highlighted several unresolved challenges, including the role of FNAB versus core needle biopsy, the definition of adequacy, the use of ancillary testing, and the need for standardized cytopathological language. Further research should focus on assessment of the reporting systems through prospective studies in a variety of resource settings to ensure international applicability, utilizing standardized data collection and statistical analysis. The Reporting Systems will need to continue their close correlation with the developing 6th edition of the WHO Tumour Classifications. Key words: fine needle aspiration biopsy cytopathology, WHO Reporting Systems, risk of malignancy, structured reporting.

Background Fine-needle aspiration cytology of axillary lymph nodes plays an established role in the staging and management of breast cancer. Squamous differentiation in breast carcinomas can be seen in metaplastic carcinomas, primary squamous cell carcinomas and treatment effects. This study reviews a cohort of metastatic breast carcinomas with squamous features in axillary lymph node aspirates. Methods A computerized search of the department pathology archives from 2016 to 2026 was performed for breast specimens with histologic evidence of squamous features matched to axillary lymph node aspirates, and malignant axillary lymph node aspirates with cytologic evidence of squamous features. Slides, reports and clinical information were reviewed. Results A total of 13 axillary lymph node aspirates were retrieved from 12 patients aged 42 to 79 years. Cellularity was variable and glandular clusters were seen in only 1 case. Keratin pearls were present in 6 cases. The majority of histologic correlates were invasive ductal carcinomas (n = 8/12), with histologic squamous differentiation in 6. There were 2 metaplastic carcinomas, 1 mixed ductal/lobular carcinoma with squamous differentiation, and 1 case with complete pathological response. Of 10 cases with biomarker status, 5 were triple-negative, 4 hormone-positive and 1 HER2-overexpressed. Conclusion Squamous morphology in axillary node aspirates should raise suspicion for metastatic breast carcinoma with squamous differentiation. This scenario is prone to gaps across clinical, histological, cytological, and immunocytochemical layers. Careful observation of subtle glandular components, accompanied by review of histological findings and immunocytochemistry, is important for accurate diagnosis.