Introduction:Breast carcinoma is the most common breast malignancy among women in Indonesia,accounting for 30.8% of female cancer cases in 2020, with high prevalence at Dr. Mohammad Hoesin General Hospital (20.9% in 2019–2020). Serum calcium plays a crucial role in cellular regulation of cancer through homeostasis of PTH, vitamin D, and mechanisms such as PTHrP and local osteolysis, where hyp…