Distinct Markers Clinical Outcomes and Driver Mechanisms in Triple Negative Breast Cancers (TNBCs)

By: Ezanee Azlina MH (ezanee.azlina.mohamad.hanif@ppukm.ukm.edu.my)

Triple negative breast cancer (TNBC) is a heterogeneous subtype of breast cancer with aggressive biology and poor clinical outcomes. TNBCs are so called because they are negative for expression of the estrogen, progesterone and Her2 receptors. To date, unlike other subtypes, there are no targeted therapies for TNBCs with current first line treatment consisting of the generic DNA damage chemotherapy cocktail (FEC). The aims of this study were (i) to identify markers of poor outcome to FEC in TNBCs and (ii) to identify genes/pathways associated with this poor biology which could represent novel therapeutic targets.

We defined ‘poor outcome’ as relapse <5 years and ‘good outcome’ as no relapse >5 years post FEC treatment. Stratifying patients based on these criteria we performed supervised clustering on 60 TNBC microarray profiles to generate a differential genelist. This yielded 114 significant genes (p<0.05, +/- 2fold), many found to be repressed in poor outcome TNBCs. We validated candidate markers in a panel of cell lines (N=9) by RqPCR (3 normal-like, 3 good outcome/Basal A and poor outcome/Basal B cell lines). Many of the validated markers possessed roles in EMT regulation and associations with mutant p53 or defective p63 signaling. Amongst these were a miRNA whose expression was reduced in non-tumourigenic cells following p63 knockdown. We also observed reduction of invasion and migration upon stable overexpression of this miRNA. Recovery of this marker was seen upon knockdown of epigenetic modifying enzymes, suggesting its expression may be influenced by the p53/p63 pathway and repression by epigenetic mechanisms.

In summary, we have identified several markers of FEC response in TNBCs with association with p53/p63-dependent regulation. Further evaluation is warranted for better understanding of how these markers are aberrantly regulated in poor outcome TNBCs and if targeting these pathways through inhibiting specific epigenetic enzymes could offer a novel therapeutic approach.