SAT259 A Rare Case Of Bisphosphonate Refractory Hypercalcemia; Cancer Masquerading As Hidradenitis Suppurativa

Disclosure: L.A. Robles: None. T. Ayub: None. I. Haque: None. C.E. Guillen Lopez, MD: None. S. Guntupalli: None. Introduction: Hypercalcemia of malignancy (HCM) associated with squamous cell carcinoma (SCC) of cutaneous origin is rare, with an estimated prevalence of 4.6%. We present a case of paraneoplastic hypercalcemia from PTHrP production by SCC arising in the setting of long-standing hidradenitis suppurativa (HS). Clinical Case: A 48-year-old male with a 20-year history of severe HS presents with concerns of disease deterioration and HS flare of buttocks, as well as, constipation, weakness, anorexia, and weight loss. Patient had recently discontinued treatment with Adalimumab for three weeks due to Covid-19 infection. Physical examination was significant for extensive hidradenitis to bilateral buttocks with granulation tissue at the base, surrounding induration, and scarring. Laboratory significant for corrected calcium 14.6 mg/dL (8.6-10.2 mg/dL), albumin 3.2, PTH 5 pg/mL(15-65 pg/mL), phosphorus 1.7mg/dL, ionized calcium 1.93 mm/L (1.15-1.30 mm/L), Vitamin D 25 mg/mL, 1,25 Vitamin D 14 pg/mL. Imaging with CT pelvis with innumerable peripherally enhancing centrally hypoattenuating lesions involving bilateral gluteus. Initially, calcium responded temporarily to IV hydration, calcitonin, and Pamidronate. Further work-up revealed PTHrP 24 pg/mL (11-20 pg/mL) and surgical pathology of bilateral buttocks with fragments of moderately to poorly differentiated SCC with perineural invasion of small caliber nerves and metastasis to lymph nodes. Patient remained significantly hypercalcemic during hospital course and received four doses of Pamidronate and eight doses of calcitonin. Diagnosis of bisphosphonate refractory hypercalcemia was established. Denosumab was given after patient became lethargic, and improvement of hypercalcemia followed. Oncology and Radiation therapy stated further treatment was not feasible given the lack of curative options and poor performance status, patient and family opted to pursue comfort care. Conclusion: Hypercalcemia presents in up to 30% of patients with malignancies and tends to predict a poor prognosis. Many mechanisms lead to HCM, with PTHrP production being the most common. Despite the prevalence of HCM, the risk of malignant transformation of HS to SCC is rare, with limited cases reported to date. Additionally, limited literature demonstrates mortality rates greater than 40% and involvement of buttocks, especially in men, exhibits the most malignant potential. Therefore, if a diagnosis of SCC in HS is made, an aggressive approach to management is advised to prevent significant morbidity and mortality. Bisphosphonates are the first-line therapy of HCM, but recent guidelines recommend treating severe HCM with a combination of calcitonin with either bisphosphonate or denosumab as the initial management. Furthermore, in those with bisphosphonate refractory HCM, treatment with denosumab would be the next step, as presented in our case. Presentation: Saturday, June 17, 2023