L26/O-115 Keep calm and preserve fertility: harnessing the power of ultrasound in differential diagnosis between endometriosis and cancer

Abstract Background Endometriosis affects approximately 10% of women of reproductive age and is associated with an increased risk of specific ovarian cancer histotypes, particularly endometrioid and clear cell carcinomas. The clinical overlap between benign endometriotic disease and potential malignant transformation represents a significant diagnostic challenge, especially in women seeking fertility preservation. In this setting, accurate preoperative assessment is crucial to balance oncologic safety with the avoidance of unnecessary radical surgery. Objective To define the role of expert transvaginal ultrasound in supporting fertility-preserving clinical decision-making across differential diagnosis, exclusion of synchronous endometrial pathology, and post-treatment surveillance. Results Expert transvaginal ultrasound is central to distinguishing typical endometriotic cysts from those requiring further oncologic evaluation. Within a structured approach such as the IOTA framework, most endometriomas present as unilocular cysts with ground glass echogenicity. However, the presence of solid vascularised components or papillary projections, particularly in large lesions (>9 cm), should raise suspicion for malignant transformation and warrant multidisciplinary assessment. Importantly, ultrasound contributes not only to lesion characterisation but also to clinical decision-making. The ability to identify reassuring features supports conservative management in selected patients, thereby avoiding unnecessary surgeries that may compromise ovarian reserve. Conversely, the recognition of suspicious features enables timely referral to oncologic care. In addition to adnexal evaluation, systematic assessment of the endometrial cavity is essential, particularly in patients with suspected endometrioid ovarian carcinoma. The exclusion of synchronous endometrial malignancy is a key step prior to considering fertility-sparing strategies, given its direct implications for staging and treatment planning. Following fertility-sparing surgery, structured follow-up is required due to the risk of recurrence. Serial transvaginal ultrasound, integrated with clinical assessment and serum biomarkers, represents the primary imaging modality for early detection of local recurrence, allowing prompt intervention while minimising overtreatment. Conclusions Expert transvaginal ultrasound plays a pivotal role throughout the clinical pathway of endometriosis-associated malignancy risk, from initial diagnosis to treatment selection and follow-up. When integrated within a multidisciplinary, guideline-based framework, it supports personalised management strategies that balance oncologic safety with preservation of reproductive potential. Its appropriate use has direct clinical implications in reducing both delayed cancer diagnosis and unnecessary loss of fertility.