SETD2 alterations and histone H3K36 trimethylation in phyllodes tumor of breast

SETD2 is one of the key epigenetic regulatory genes involved in histone modifications. Its alterations were potentially oncogenic and commonly found in cancers. Interestingly, SETD2 is one of the most frequent mutated genes found exclusively in phyllodes tumor of the breast (PT). However, little has been done to further characterize SETD2 alterations in PT.

In this study, we examined the alterations of SETD2 gene and protein expression in a large cohort of PTs. Their correlations with SETD2 downstream target, H3K36me3 expression, and clinicopathologic features in PT were also assessed.

SETD2 mutation was found in 15.9% of our cases and was mostly predicted to be damaging mutations. Interestingly, SETD2 mutations were associated with lower H3K36me3 expression, particularly those with damaging mutations (p = .041). Neither SETD2 mutations nor H3K36me3 expression was associated with PT grading and other clinicopathological features. By contrast, the SETD2 protein expression cannot reflect its mutation status and showed a different trend of clinicopathological correlations from H3K36me3.

Our findings may suggest a potential involvement of epigenetic regulation via SETD2 alterations and downstream H3K36me3 on PT development. SETD2 mutations may occur early in the pathogenic process of PTs and its loss per se may not be sufficient for progression to malignancy. Exclusive alterations of SETD2 in PT can be used as markers for the diagnosis of fibroepithelial lesions. The association of H3K36me3 with SETD2 mutations may also indicate the value of evaluation of H3K36me3 expression in the diagnosis of fibroepithelial lesions.