Abstract
BACKGROUND: Cetuximab sarotalocan, which utilizes the light-activatable dye IRDye700Dx conjugated with cetuximab, is a first-in-class drug based on photoimmunotherapy for treating recurrent head and neck squamous cell carcinoma. Cetuximab frequently induces hypomagnesemia and secondary hypocalcemia. Herein, we report a case of independent hypocalcemia without hypomagnesemia during treatment and discuss symptom progression. CASE PRESENTATION: A female patient with left epipharyngeal cancer, hypothyroidism, and hypoparathyroidism was treated with cetuximab and sarotalocan. On day 3, serum-adjusted calcium levels decreased from 9.6 to 7.4 mg/dL, increased to 8.2 mg/dL on day 9, and further increased to 8.8 mg/dL on day 27; serum magnesium levels were not evaluated. After the second administration, serum-adjusted calcium levels decreased two days later, fluctuating between 7.6 and 8.1 mg/dL for three weeks. Serum magnesium levels were within the normal range, with no significant variation detected during the second cycle. A similar symptom course was observed during the third cycle. The patient received enteral nutrition daily with 424.8-1,038.4 mg of calcium, with daily adjustment during the administration, except on day 2. She received peripheral intravenous nutrition for several days after tumor illumination. Concomitant medications did not appear to affect serum calcium levels. Considering the case process and previous reports, we hypothesized that concomitant hypoparathyroidism, in addition to reduced calcium intake due to the treatment, may have contributed to the observed reduction. CONCLUSIONS: Hypocalcemia without hypomagnesemia can occur in patients with hypoparathyroidism receiving near-infrared photoimmunotherapy with cetuximab sarotalocan. The precise mechanisms and epidemiological features warrant further investigations.