19q12 amplified and non-amplified subsets of high grade serous ovarian cancer with overexpression of cyclin E1 differ in their molecular drivers and clinical outcomes.

OBJECTIVES

Readily apparent cyclin E1 expression occurs in 50% of HGSOC, but only half are linked to 19q12 locus amplification. The amplified/cyclin E1 subset has intact BRCA1/2, unfavorable outcome, and is potentially therapeutically targetable. We studied whether non-amplified/cyclin E1 HGSOC has similar characteristics. We also assessed the expression of cyclin E1 degradation-associated proteins, FBXW7 and USP28, as potential drivers of high cyclin E1 expression in both subsets.

METHODS

262 HGSOC cases were analyzed by in situ hybridization for 19q12 locus amplification and immunohistochemistry for cyclin E1, URI1 (another protein encoded by the 19q12 locus), FBXW7 and USP28 expression. Tumors were classified by 19q12 amplification status and correlated to cyclin E1 and URI1 expression, BRCA1/2 germline mutation, FBXW7 and USP28 expression, and clinical outcomes. Additionally, we assessed the relative genomic instability of amplified/cyclin E1 and non-amplified/cyclin E1 groups of HGSOC datasets from The Cancer Genome Atlas.

RESULTS

Of the 82 cyclin E1 cases, 43 (52%) were amplified and 39 (48%) were non-amplified. Unlike amplified tumors, non-amplified/cyclin E1 tumor status was not mutually exclusive with gBRCA1/2 mutation. The non-amplified/cyclin E1 group had significantly increased USP28, while the amplified/cyclin E1 cancers had significantly lower FBXW7 expression consistent with a role for both in stabilizing cyclin E1. Notably, only the amplified/cyclin E1 subset was associated with genomic instability and had a worse outcome than non-amplified/cyclin E1 group.

CONCLUSIONS

Amplified/cyclin E1 and non-amplified/cyclin E1 tumors have different pathological and biological characteristics and clinical outcomes indicating that they are separate subsets of cyclin E1 HGSOC.