Molecular characterisation incorporating immunohistochemical assessment of p53 and MMR protein expression now plays a critical role in the classification and management of female genital tract tumours, particularly in cases of endometrial carcinoma. With increasing use of these markers, unusual or discordant staining patterns can be seen that can represent pitfalls and/or generate diagnostic uncertainty. This session will cover a selection of such cases aiming to highlight how the integration of morphological, immunohistochemical and molecular results can help avoid misclassification and ensure appropriate treatment for our patients.

Gestational trophoblastic disease encompasses a spectrum of lesions ranging from hydatidiform moles to gestational trophoblastic neoplasia. Accurate diagnosis is essential, as it directly influences patient counselling, follow-up, and clinical management. However, distinction between complete mole, partial mole, non-molar hydropic pregnancy, and trophoblastic tumours can be challenging, particularly in early gestations or limited specimens.

This talk will provide a practical approach to the histopathological diagnosis of gestational trophoblastic disease, highlighting key morphological features, common diagnostic pitfalls, and useful ancillary tests. Emphasis will be placed on recognising patterns of villous abnormality, assessing trophoblastic proliferation, and applying p57 immunohistochemistry appropriately. The role of molecular genotyping in resolving difficult cases will also be discussed.

Through practical tips and illustrative examples, this session aims to improve diagnostic confidence and promote a structured approach to gestational trophoblastic lesions in routine practice.