Abstract
Uterine leiomyosarcomas frequently show p16 immunoexpression. However, p16 may also be expressed in some benign leiomyoma variants such as leiomyomas with bizarre nuclei and cellular leiomyomas, limiting its utility as a biomarker to distinguish between benign and malignant neoplasms. We investigated p16 expression in leiomyomas with infarct-type necrosis, tumours which may sometimes be misinterpreted as smooth muscle tumours of uncertain malignant potential or even leiomyosarcoma on conventional light microscopy. p16 immunostaining was performed on 35 leiomyomas with infarct-type necrosis and the staining pattern was analysed. Staining was classified as absent, scattered/isolated, <33-, 33-66- or >66%-positive cells, and was assessed in the areas immediately surrounding and distant from the infarct. The median age of patients was 44 years. Seventeen had hormonal/non-hormonal drugs and three were pregnant. The median tumour size was 7.25 cm. The mean mitotic count was 0.9/10 high-power fields. Only one tumour had multifocal mild nuclear atypia. Positive p16 was noted in 34 of 35 (97.2%) tumours. It was typically patchy, and was concentrated in areas immediately surrounding the necrosis. Distant from the necrosis, p16 positivity was seen predominantly in scattered/isolated cells. One tumour without any worrisome microscopic features showed diffuse p16 positivity throughout. Median follow-up was 55 months, and none of the patients experienced any recurrence. p16 expression in benign uterine smooth muscle tumours with infarct-type necrosis is common. The staining is particularly concentrated adjacent to areas of necrosis. It is important to be aware of this potential pitfall when interpreting p16 expression.
Published Version
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