P5-03-01: Cytoplasmic Cyclin E and P-CDK2 Expression in Triple Negative Breast Carcinomas Measured by Immunohistochemistry Correlates with Poor Outcome.

Background: Triple negative breast carcinomas (TNBCs) are aggressive malignancies that lack effective therapeutic targets but express low molecular isoforms of cyclin E (LMW-E). These LMW-E, generated primarily from NH2-terminal elastase cleavage of full length cyclin E (EL), preferentially accumulate in the cytoplasm of cancer cells. Using a transgenic mouse model system, our laboratory has recently shown that cyclin-dependent kinase 2 (CDK2) is required for LMW-E-mediated mammary tumorigenesis. These results lead us to hypothesize that immunohistochemical cytoplasmic detection of LMW-E and phospho-CDK2 in TNBC provides a valuable screening tool for those patients most likely to have a poor prognosis who could then be treated with anti-CDK2 therapy currently clinically available. Material and Methods: Tissue micro-arrays from 168 TNBC patients were IHC stained for cyclin E and p-CDK2. Cyclin E staining intensity and percentage of positivity were evaluated both in the nucleus and cytoplasm of cancer cells and four different phenotypes of cyclin E were distinguished with respect to predominant nuclear or cytoplasmic localization of staining: cyclin E negative, predominantly nuclear, both nuclear and cytoplasmic and predominantly cytoplasmic. p-CDK2 IHC was achived using an antibody, which recognizes phospho-threonine 160 on CDK2. Immunoreactive scores were determined by multiplying the intensity with the extent of staining of nuclei and cytoplasm. We sought correlations between different cyclin E and p-CDK2 expression patterns and disease-free survival (DFS). Results: Cytoplasmic cyclin E accumulation on IHC of TNBCs correlated with poor outcome. Within the median follow up of 7.3 years tumors with both nuclear and cytoplasmic cyclin E expression demonstrated higher recurrence rate compared to entirely negative for cyclin E (p=0.0117). In contrast patients with exclusively nuclear cyclin E showed only a trend toward decreased DFS compared to patients with cyclin E negative tumors (p=0.0896). Furthermore we identified the new phenotype of cyclin E immunoreactivity, which is characterized by negative nucleus and positive cytoplasmic staining. This phenotype was the most significantly associated with poor DFS compared to cyclin E negative phenotype (p=0.0026) and as the only one distinguished at high risk of early recurrence among TNBC patient without axillary nodes involvement (p=0.0105). The expression of p-CDK2 was significantly higher in this phenotype than the cytoplasmic cyclin E.negative tumors. High p-CDK2 tumors were also correlated to worse DFS then p-CDK2 low tumors (P=0.019). Lastly, our analyses revealed that tumors positive for both cytoplasmic cyclin E and p-CDK2 had higher recurrence rate compared to negative for both or positive for one of them (p=0.003). Discussion: Cytoplasmic cyclin E may help to predict recurrence, especially in early stage, node negative TNBCs. We present a new concept in assessing cyclin E expression. Poor outcome due to TNBCs overexpressing LMW-E provide a rationale to investigate the treatment strategies that could specifically target high LMW-E tumors. These patients could particularly benefit from treatment with CDK2 inhibitors. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-03-01.