High receptor activator of Nuclear Factor Kappa β (RANK) expression and luminal A subtype are associated with bone metastasis in patients with breast cancer

Introduction: Bones are the most common distant metastasis site in breast cancer, especially in advanced stages. Bone metastasis involves continuous interaction between tumor cells, osteoblast, osteoclast, and bone matrix.There are many risk factors regarding distant metastasis sites in breast cancer patients, including breast cancer molecular subtypes and mediator known as Receptor Activator of Nuclear Factor Kappa beta (RANK). In this study, we explore relationships between Luminal A breast cancer and RANK in association with bone metastasis site. Method: This study is a cross-sectional analysis study conducted in Sanglah General Hospital, Bali Denpasar. The estimated sample size was measured using formula to hypothesize between two proportions and obtained 34 patients as our minimal sample needed in this study. Data will be presented in 2x2 tables, consist of RANK Protein expression and molecular cancer subtype (Luminal A / Non-Luminal A) in row section and Metastasis (Bone Metastasis or Non-Bone Metastasis) in column section. Univariate analysis was done using a comparative method between 2 categorical unrelated groups: Chi-Square and Fisher's Exact Test. OR values were measured, and p-value <0.05 considered to be significant statistically. Result: From these 106 patients, we used nested sampling to randomize these patients into our study sample, with a total of 36 patients. The mean age of our patients is 48.64 +/- 9.86 years. Luminal A subtypes tend to metastasize into bone component compared with Non-Luminal A subtypes with p-value 0.041 and OR: 3.5; with 95% CI (0.82 - 14.84). Tumor with high-RANK expressions tends to metastasize into bone component compared with low-RANK expressions with p-value 0.045 and OR 3.25; with 95% CI (0.81 - 13.03) Conclusion: There is a significant difference statistically in molecular subtype breast cancer and RANK protein expressions between two patient groups (bone metastasis site vs. other metastasis sites).