PTEN-deficient breast cancer in neoadjuvant treatment.

1125 Background: Loss of function mutations in the tumour suppressor gene PTEN or lack of PTEN expression have both been observed in a wide range of human tumours. PTEN encodes a phosphatase, whose activity antagonizes PI3 kinase signal pathway by dephosphorylation the plasma membrane lipid, phosphoinositide-3,4,5-trisphosphate (PIP3). Loss of PTEN phosphatase activity is thought to foster tumorigenesis, at least in part, by causing downstream constitutive activation of AKT. In addition to this role, PTEN has been suggested to have a nuclear function in maintaining genomic stability[2]. Our proposal is to identify those tumours without expression of PTEN, their characteristics and response to treatment. Methods: We have studied PTEN expression by immunohistochemistry in tumours samples from 86 patients treated with neoadjuvant treatment. Normal breast epithelium or vascular endothelium were used as positive control. PTEN was evaluated by inmunoreactive stain score, taking into account staining intensity and percentage of positive cells, PTEN deficiency (PTEN -) has been stablished by a IRS=0[1]. We analyzed the PTEN localization (nuclear vs citoplasmatic). Results: In our serie, 38 (44.2%) of the tumours samples were PTEN deficient. Taking into account as reference PTEN + tumours, we have found that PTEN deficient tumours are more frequently; ductal carcinoma (94.2% vs 81.8%), G3 (72% vs 48.7%), ER negative (47% vs 30.4%), Triple negative (24.2% vs 15%) and higher Ki67 expression (>20%) in the 100% of PTEN deficient tumours. The pathological rate response was PTEN -:18.4% vs PTEN +:19.1% p:ns, and the recurrence rate was higher in PTEN- (26,3% vs 8,3%) p:0.025. Conclusions: The PTEN deficient breast tumours is associated to more histological aggressive profile, and we have not found relations with the pathological rate response to neoadjuvant treatment.