SUN-791 Hypercalcemia Concealed Under a Wound: An Unsuspecting Case of Metastatic Squamous Cell Carcinoma

Abstract Disclosure: K. Winnicki: None. G. Olson: None. E. Rosario Diaz: None. R.I. Mateo: None. Background: Marjolin's ulcer is a rare cutaneous malignancy that arises in areas of previously traumatized or chronically inflamed skin; this is an underrecognized cause of hypercalcemia. Case: A 52-year-old male with a history of paraplegia, chronic osteomyelitis, neurogenic bladder, bilateral hydronephrosis, and a stage IV sacral pressure ulcer presented for ureteral stent exchange. He was found to be hypercalcemic to 12 mg/dL (adjusted calcium 9.1 - 11.2 mg/dL) with ionized calcium 1.43 mmol/L (0.95 - 1.32 mmol/L). He did not endorse symptoms associated with hypercalcemia but did report taking calcium supplements. PTH was suppressed at 10.9 pg/mL (8.0 - 85.0 pg/mL), and 25-hydroxy vitamin D was 5 ng/mL (>20 ng/mL). Protein electrophoresis was unremarkable, PTHrP was undetectable, and 1,25 vitamin D was 11.3 pg/mL (24.8 - 81.5 pg/mL). The supplements were discontinued and aggressive IV fluids were initiated, however, after several days of robust urine output, the ionized calcium continued to rise to a peak of 1.56 mmol/L (0.95 - 1.32). The patient had no change in his mobility and prior admissions for osteomyelitis did not show any lab findings of hypercalcemia. CT scans revealed extensive destructive bony changes of the pelvis and bilateral femurs as well as small hypodensities of the liver and lung. Re-evaluation of the patient’s sacral wound revealed a large, indurated region. Tc-99m scan revealed heterogeneous uptake in the pelvis, with moderately intense diffuse patchy uptake in the left hip joint region extending to the proximal left femur and left hemipelvis, which correlated with destructive areas on CT. The large indurated sacral wound overlaid this region. Both liver and sacral wound were biopsied and positive for squamous cell carcinoma; a clinical diagnosis of metastatic Marjolin’s ulcer was made. He received IV zoledronic acid with eventual normalization of ionized calcium to 1.05 mmol/L (0.95 - 1.32) and was also subsequently started on vitamin D to reduce risk of post-bisphosphonate hypocalcemia. Treatment with cemiplimab was initiated, and consultation with orthopedics was recommended but unfortunately no other surgical options were offered at this time. Hall and colleagues previously described a case of hypercalcemia complicating Marjolin’s ulcer in a patient with quadriplegia and chronic osteomyelitis without PTHrP elevation, suggesting cytokine production and transforming growth factor alpha as a possible mechanism [1]. In this case, we suspect invasion of overlying squamous cell carcinoma into bone with further destruction was the likely mechanism of hypercalcemia. Conclusion: We further support that unexplained hypercalcemia in patients with longstanding sacral wounds should raise the suspicion for Marjolin’s ulcer as a possible etiology. [1] Hall AB, Buehler KE, Philipneri M. Hypercalcemia complicating Marjolin's ulcer. Mil Med. 2009 Mar;174(3):308-10. Presentation: Sunday, July 13, 2025