PRR11 expression in early ER+/HER2‑low breast cancer: Association with estrogen receptor positivity and exploratory analysis of prognostic significance

The present study aimed to investigate proline‑rich protein 11 (PRR11) expression and to exploratorily assess its prognostic relevance in early estrogen receptor (ER)+/HER2‑low breast cancer. Data of 124 patients with early ER+/HER2‑low breast cancer were evaluated retrospectively. PRR11 expression was analyzed in tumor tissues and reported as the median fold change relative to the cohort median. PRR11 expression was comparatively analyzed in subgroups according to ER percentages in 10% intervals and HER2‑low status: CerbB2 immunohistochemistry (IHC) +1 (n=66) and +2 (n=58). PRR11 expression analysis was also performed in the residual tumors of patients who received neoadjuvant chemotherapy (NAC; n=14) and patients without pathological complete response (pCR; n=11). The median PRR11 expression fold change was 0.31 in the ER (1‑10%) subgroup, 0.50 in the ER (20‑30%) subgroup, 1.19 in the ER (40‑50%) subgroup, 1.23 in the ER (70‑80%) subgroup, 1.41 in the ER (80‑90%) subgroup and 1.55 in the ER (>90%) subgroup. The median fold change in PRR11 expression was 1.717 in the CerbB2 IHC 1+ subgroup and 0.999 in the CerbB2 IHC 2+ subgroup. PRR11 expression was decreased in 4 patients (36%) and increased in 7 patients (64%) after NAC. Kaplan‑Meier survival analysis stratified by PRR11 expression did not indicate a statistically significant difference in 5‑year disease‑free survival (DFS) or overall survival between the high‑ and low‑PRR11 expression groups. Receiver operating characteristic analysis of DFS yielded an area under the curve of 0.409 (optimal cut‑off, 0.18; sensitivity, 100%; specificity, 15.3%), indicating no meaningful discriminatory value. There was a positive association between PRR11 expression and the ER positivity rate. Higher PRR11 levels in residual tumors of non‑pCR patients represented a preliminary, hypothesis‑generating observation regarding the potential predictive value of PRR11 in patients receiving NAC. Randomized clinical trials are needed in this area.