Poster Presentation ESA-SRB-APEG-NZSE 2022

Hypocalcaemia in malignancy: A case of prostate cancer with osteoblastic metastases (#320)

Arunan Sriravindrarajah 1 2 , Beryl Lin 2 3 , Jessica Bindra 1 4 , Alison Zhang 2 3 5 6 , Stephen Twigg 1 2 7
  1. Department of Endocrinology and Metabolism, Royal Prince Alfred Hospital, Sydney, NSW, Australia
  2. Faculty of Medicine and Health, University of Sydney, Sydney, NSW, Australia
  3. Royal Prince Alfred Hospital, North Sydney, NSW, Australia
  4. School of Medicine, Western Sydney University, Sydney, NSW, Australia
  5. Faculty of Medicine, Macquarie University, Sydney, NSW, Australia
  6. Chris O'Brien Lifehouse, Sydney, NSW, Australia
  7. Charles Perkins Centre, University of Sydney, Sydney, NSW, Australia

Background: Prostate cancer is the most common non-skin cancer in Australian men.1.2 Metastatic prostate cancer may be associated with osteoblastic lesions that consume calcium for bone formation.3

Case: A 77-year-old Caucasian male was admitted with gastrointestinal bleeding on a background of bowel telangiectasia, castrate-resistant metastatic prostate cancer (BRCA2-associated) and oesophageal cancer in remission. Blood tests identified a new onset asymptomatic hypocalcaemia that was not present on admission, with corrected calcium 1.92mmol/L, ionised calcium 0.99mmol/L, phosphate 0.62mmol/L, magnesium 0.88mmol/L, PTH 23.3pmol/L, eGFR>90mL/min, 25OH vitamin D 18nmol/L, and ALP 174U/L. Whilst he had received subcutaneous Denosumab 120mg, his serum calcium levels were initially within normal range and only declined 30 days following administration. Serum calcium levels remained low despite cessation of PRBC transfusions, replacement of 25OH vitamin D deficiency, hypocalciuria (calcium-to-creatinine ratio <0.1mmol/mmol) and treatment of prostate cancer with Docetaxel and androgen deprivation therapy with Leuprorelin and Enzalutamide. PSMA-PET and CT chest, abdomen and pelvis confirmed the presence of extensive sclerotic bony metastases with multiple pathological fractures. Further investigations identified significant elevations in PSA 2,162ug/L (0.3-7.5), bone formation marker P1NP 185ug/L (15-115), and bone resorption marker urine DPD 5.9nmol/mmol (2.3-5.4), which is consistent with bone formation of osteoblastic metastases. Treatment with Caltrate 1200mg TDS, calcitriol 0.5mcg QID and cholecalciferol 5000IU daily was required to achieve and maintain normocalcaemia. Due to poor functional status, he was not suitable for further anti-cancer therapy. He was re-admitted with gastrointestinal bleeding and experienced a cerebrovascular accident. Unfortunately, his condition deteriorated, and he died upon transition to comfort care.

Conclusion: This case demonstrates osteoblastic metastases as an atypical cause of hypocalcaemia. Added contributors such as vitamin D deficiency with anti-resorptive usage need to be considered. Without effective prostate cancer treatment that could reverse osteoblastic metastases, there will be ongoing hypocalcaemia and requirement for high dose calcium replacement.

  1. Understanding Prostate Cancer. Cancer Council. 2022. [online] Available at: https://www.cancer.org.au/assets/pdf/understanding-prostate-cancer-booklet [Accessed 16 August 2022].
  2. Prostate cancer in Australia statistics. Cancer Australia. 2022. [online] Available at: https://www.canceraustralia.gov.au/cancer-types/prostate-cancer/statistics [Accessed 16 August 2022].
  3. Severe hypocalcaemia associated with extensive osteoblastic metastases in a patient with prostate cancer. Fokkema et. al. 2005, Neth J Med. 63(1): 34-7.