An endometrial thickness of <12 mm does not exclude malignancy or pre-malignancy in cases of abnormal uterine bleeding: An observational study.

Background: It remains unclear if there is an endometrial thickness (ET) threshold below which malignancy can be excluded. Guidance on whether endometrial biopsy is needed based on ET varies among regions in New Zealand and there is a desire to standardise guidance nationwide. This study evaluates the potential impact of limiting endometrial biopsy in pre-menopausal persons with abnormal uterine bleeding (AUB) to those with an ET of less than 12 mm.

Aims: To determine the number of pre-menopausal patients with AUB with an ET of less than 12 mm undergoing endometrial sampling annually and assess the prevalence of pathology among these patients.

Materials And Methods: Endometrial samples from patients aged 18-50 years processed at a tertiary hospital between 15/06/2022 and 13/06/2023 were identified via a pathology lab search. Clinical, radiologic, and pathological data were obtained by case note review for those with AUB whose ET was less than 12 mm.

Results: Of 1271 endometrial samples, 355 patients met the eligibility criteria, and 2.2% of these were cancerous (three cases) or pre-malignant (five cases).

Conclusions: If sampling thresholds would change to not perform biopsies in those with an ET of less than 12 mm, eight cases of treatable disease would be missed in pre-menopausal people. This represents 13.6% of all endometrial cancers diagnosed in pre-menopausal people in the same time period. There is no ET cut-off to reliably exclude high-risk pathology and endometrial sampling should be performed in all cases of AUB with risk factors.