• Snježana Ramić, Frane Paić, Velda Smajlbegović, Melita Perić Balja, Lea Hiršl, Ingrid Marton, and Fabijan Knežević.
• Frane Paić, Laboratory for Epigenetics and Molecular Medicine, Department of Biology and Medical Genetics, School of Medicine, University of Zagreb, Šalata 3, 10 000 Zagreb, Croatia, fpaic@mef.hr.
• Croat. Med. J. 2022 Apr 30; 63 (2): 126-140.

AimTo determine the predictive value of phosphorylated human epidermal growth factor receptor 2 (pHER2Y1248) status in breast cancer (BC) patients undergoing trastuzumab-based adjuvant therapy.MethodsImmunohistochemical status of pHER2Y1248, EGFR/HER1, HER3, and HER4 was determined in 124 consecutive HER2-positive BC patients (median age [range]=57 years [49.0-64.0]) treated at the University Hospital for Tumors, Zagreb, between 2008 and 2011. The median follow-up was 84 months (60.0-84.0). Prognostic factors of disease free survival (DFS) rate were evaluated with Kaplan-Meier/log-rank test and Cox regression analysis.ResultspHER2Y1248, HER1, HER3, and HER4 were expressed in 66.1%, 9.7%, 70.2%, and 71.0% of patients, respectively. Disease progression (DP) was observed in 17.1% of pHER2Y1248-positive and 47.6% of pHER2Y1248-negative BCs (P=0.001). Kaplan-Meier analysis showed a worse five-year DFS in pHER2Y1248-negative patients who were older than 60 years (P<0.001) and had positive lymph node status (P<0.001); tumor size >2.0 cm (P<0.001); higher histological grade (P<0.001); HER2E intrinsic subtype (P<0.001), negative hormone receptors (P<0.001); negative HER1 status (P<0.001), positive HER3 (P=0.002); and/or positive HER4 (P=0.002) status. The only negative prognostic factor for five-year DFS in multivariate Cox regression analysis was pHER2Y1248-negative (hazard ratio [HR] 3.6, 95% confidence interval [CI] 1.8-7.2, P<0.001) and lymph node-positive status (HR 3.6, 95% CI 1.3-9.8, P=0.014).ConclusionpHER2Y1248 predicts sensitivity to trastuzumab and a better five-year DFS regardless of any other prognostic parameter. In HER2-positive BC patients. Non-phosphorylated HER2Y1248 is a strong predictor of trastuzumab resistance and a poor DFS.

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