Apolipoprotein C1 expression in molecular subtypes of breast cancer: clinical correlation and prognostic significance

Background: Breast cancer includes a wide spectrum of tumors with different morphological, molecular, and clinical phenotypes. Further discovery of new prognostic markers with therapeutic implications is warranted. Apolipoprotein C1 (APOC1) is a member of the apolipoprotein family located on chromosome 19 and participates in lipid transport and metabolism. Recently, some studies have explored its association with cancer development. Material and Methods: In this study, we aimed to study APOC1protein expression in molecular classes of breast carcinoma and to correlate its expression with other clinicopathologic variables using immunohistochemistry and tissue microarrays in 200 cases of breast cancer in Egyptian women. Results: High to moderate APOC1 cytoplasmic expression was observed in 57.5% of the cases. APOC1 expression was common in ER-negative and PR-negative cases in comparison to positive cases (P<0.001), while it was common in HER2-positive cases (P<0.001). Positive APOC1 cases showed a higher Ki67 proliferation index. Expression of APOC1 was more common in ductal followed by the lobular tumor type (P=0.002). Triple-negative basal-like breast cancer. (BLBC) showed the highest expression of APOC1, while the luminal A subtype showed the lowest expression level (P<0.001). Expression of APOC1 was more common in cases with recurrence than in cases without recurrence. Survival analysis showed that APOC1 was a significant prognostic marker for overall survival (log rank: 5.87, P=0.015) and disease-free survival (log rank: 15.86, P<0.001). Multivariate Cox regression analysis mortality showed that APOC1 is an independent prognostic marker with a hazard ratio of 1.47, confidence interval=1.08–1.99, and P value of 0.014. Conclusion: Our study showed a strong association between high APOC1 expressions and triple-negative basal-like breast cancer. APOC1-positive breast cancer showed a significantly shorter overall survival and disease-free interval. APOC1 is an independent predictor of mortality in our patient cohort supporting its role in breast cancer progression and highlighting its potential therapeutic implications.