Abstract
BACKGROUND/AIM: Breast cancer remains a significant health challenge, with neoadjuvant chemotherapy (NACT) improving clinical outcomes in certain subtypes. However, the role of NACT in hormone receptor-positive, HER2-negative (HR+/HER2-) breast cancer is unclear due to various outcomes and generally low rates of pathologic complete response (pCR). This study introduces the Non-Luminal Disease Score (NOLUS) as a potential predictive tool for assessing the response to NACT in these cases. PATIENTS AND METHODS: We retrospectively assessed patients diagnosed with locally advanced HR+/HER2- breast cancer who received NACT at our institution from 2009 to 2023. The study explored the association between NOLUS and pCR rates. NOLUS was calculated as positive or negative based on the percentage of estrogen receptor, progesterone receptor, and Ki-67 in tumor cells. We also investigated the correlation between pCR and invasive disease-free survival (iDFS), and examined NOLUS positivity across different age groups. RESULTS: A total of 149 patients met the inclusion criteria. NOLUS-positive patients exhibited a significantly higher pCR rate of 33.33% compared to 10.4% in NOLUS-negative patients (p=0.0031). With a median follow-up of 2.47 years, NOLUS-positive patients who achieved pCR had a 100% iDFS rate, mirroring the pCR versus residual disease patterns seen in triple-negative patients. NOLUS positivity was observed in 20.43% of patients aged 22-50, compared to 8.93% in those over 50, though this difference was not statistically significant. CONCLUSION: NOLUS exhibits potential in predicting pCR in HR+/HER2- breast cancer, serving as a cost-effective substitute for genomic tests.