The relationship between PRR11 expression and prognosis in early ER+/HER2 low breast cancer.

e15154 Background: We aimed to investigate the prognostic value of proline-rich protein 11 (PRR11) expression in early ER+ / HER2 'low' breast cancer (eBC). Methods: 124 ER+/HER2 'low' eBC patients at our center were evaluated retrospectively. PRR11 expression was analyzed in tumor tissues & marked as 'median fold change'. PRR11 expression was comparatively analyzed separately in subgroups according to ER percentages as 10% intervals and HER2 ‘low’ status: CerbB2 IHC +1 (n=66), +2 (n=58) scores. PRR11 expression analysis was also performed in the residual tumor of patients who received neoadjuvant chemotherapy (NAC) (n=14) and in those with non-pCR (n=11). Results: There was no difference for the patients with CerbB2 IHC 1+ and 2+, in terms of ER groups (p = 0.404). There was a positive correlation between ER positivity rate and PRR11 expression. It was striking when ER was >40%. Median PRR11 fold change were as 0.31 for ER (1-10%), 0.50 for ER (20-30%), 1.19 for ER (40-50%), 1.23 for ER (70-80%), 1.41 for ER (80-90%) and 1.55 for ER (>90%) subgroups. While median fold change for PRR11 was 1.717 in the CerbB2 IHC 1+ subgroup, it was 0.999 for the CerbB2 IHC 2+ subgroup (p=0.39). pCR rate was 21.4%. PRR11 expression was decreased in 4 patients (36%) and increased in 7 (64%) patients after neoadjuvant systemic treatment. There was no survival difference according to CerbB2 IHC scores or ER % ranges. 5 year DFS was 92.3% for CerbB2 IHC 1+ & 92.3% for CerbB2 IHC 2+ (p=0.317). It was 70% for ER (1-50%), 93% for ER (51-89%) & 94.6% for ER (>90%) (p=0.213). Conclusions: There was a positive correlation between PRR11 expression & ER positivity rate in ER+/HER2 'low' early-stage breast cancer, but it did not affect survival, probably due to small number of cases. Higher PRR11 levels in residual tumor of non pCR patients led to the consideration of its potential prognostic and predictive value for the patients on NAC. Randomized clinical trials are needed in this area.