Association between GPRC5A expression and carboplatin efficacy in triple-negative breast cancer patients.

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e13142 Background: Triple-negative breast cancer (TNBC) patients often face a grim prognosis, primarily due to their resistance to chemotherapy. Carboplatin is a common treatment for TNBC, particularly effective in BRCA1/2 mutations, but its efficacy varies in BRCA1/2 wild-type patients. A previous study identified GPRC5A expression as a biomarker for carboplatin chemotherapy in ovarian cancer, yet its association with carboplatin efficacy in TNBC remains unknown. This study aims to investigate whether GPRC5A can serve as a biomarker for predicting carboplatin efficacy in TNBC and to elucidate the underlying mechanisms. Methods: Analyzing clinical data from the past 5 years in Division of Breast & Thyroid Surgery in Jiangsu Province Hospital, we identified 199 TNBC patients treated with carboplatin. GPRC5A expression in TNBC tumors was assessed via immunohistochemistry (IHC) and evaluated by three individual pathologists. Expression levels were categorized as low (low), low (mild), high (moderate), and high (high). The Chi-square test was employed to assess the correlation between GPRC5A expression and carboplatin efficacy. TNBC-derived organoids were used to validate the relationship between GPRC5A expression and carboplatin sensitivity. Results: Among the 199 TNBC patients, 31 (17.2%) had BRCA1/2 mutations. The pathologic complete response (pCR) rate in BRCA1/2 mutation patients receiving carboplatin was 83.9%, compared to 61.3% in BRCA1/2 wild-type patients (p=0.016). Analyzing the relationship between GPRC5A expression and BRCA1/2 gene mutations in 145 patient samples revealed no significant association (p=0.37). Irrespective of BRCA1/2 mutation status, patients with low/mild GPRC5A expression had a higher pCR rate (74.1%) compared to those with moderate/high GPRC5A expression (45%, p<0.001). TNBC-derived organoids treated with carboplatin showed a cell survival rate of 31.25% (±8.5%) in low GPRC5A expression organoids and 56.25% (±12.6%) in high GPRC5A expression organoids (p=0.017). Conclusions: Our study demonstrates a correlation between GPRC5A expression and BRCA1/2 mutation status in TNBC. Furthermore, TNBC patients with low GPRC5A expression exhibited a more favorable response to carboplatin treatment, suggesting GPRC5A could be a potential biomarker for predicting carboplatin efficacy in TNBC patients.

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