142P The predictive value of progesterone receptor expression on pCR following neoadjuvant chemotherapy in breast cancer

The efficacy of neoadjuvant chemotherapy (NAC), as measured by the pathological complete response (pCR), varies between molecular subtypes in breast cancer (BC). Oestrogen receptor (ER)-positive, human epidermal growth factor 2 (HER2)-negative patients tend to have lower pCR rates. transcription progesterone (PR) is dependent on ER therefore PR negativity may suggest an erroneous oestrogen signalling pathway rendering resistance endocrine therapy. PR- tumours be more aggressive but chemosensitive. This study aimed determine if status, no longer routinely tested ER+ BC UK, can identify which ER+/HER2- will achieve pCR. would enable appropriate selection for NAC. Patients undergoing NAC at Royal Victoria Infirmary, Newcastle, 2013 and 2021 were identified their clinicopathological features collated a retrospective dataset. status was ascertained with standard immunohistochemistry. score correlated rate. Overall survival (OS) disease-free (DFS) calculated against 244 included analysis (78 triple-negative (TNBC); 25 ER+/HER2-; 141 HER2+). In group, achieved higher rates compared PR+ (31% 9%; χ2; p=0.327). rate ER+/HER2-/PR- group not statistically different that TNBC 29%; Fisher’s exact test; p=1.000). ER+/HER2+ than (23% 4%; p=0.090). (52% 24%; p = 0.015) when comparing patients. Oncological outcomes significantly improved (DFS 0.005; OS 0.032). both subtypes. behave like TNBCs hormone-positive BCs require chemotherapeutic strategies. has value determining might benefit from oncological outcomes.