SAT-723 Challenges in Endocrine Function Testing During Clinical Cancer Drug Trials: False Positives Due to Heterophilic Antibodies

Abstract Disclosure: D. Kim: None. Y. Hwang: None. S. Park: None. H. Jang: None. J. Rim: None. S. Lee: None. Y. Rhee: None. Background: The rapid advancement of clinical cancer drug development, particularly in immunotherapy, targeted therapies, antibody-based treatments, and personalized medicine, aims to improve efficacy and precision. However, the condition of cancer patients and their treatments can often impact endocrine function testing, complicating result interpretation.Clinical Cases: A woman in her mid-60s, diagnosed with stage IVb ovarian cancer, received chemotherapy (Genexol and Neoplatin), debulking surgery in March 2023, and additional chemotherapy cycles. In February 2024, brain recurrence was detected, and she underwent radiotherapy. She was referred to the Endocrinology Department for osteoporosis management, and after evaluation, she was treated with Denosumab and cholecalciferol. Six months later, during follow-up, calcium and vitamin D levels were normal, but her PTH increased from 36.1 pg/mL to 2011 pg/mL. Two months after switching to alendronate, PTH was measured at 1171 pg/mL. However, after removing heterophilic antibodies, the PTH level was 36.4 pg/mL. Following the initiation of osteoporosis treatment, the patient participated in a clinical trial to assess the safety and efficacy of Oregovomab in combination with Paclitaxel, Carboplatin, and Bevacizumab. Given that Oregovomab is a mouse monoclonal antibody, it is believed that this caused interference from heterophilic antibodies. In another patient who received Oregovomab, was referred to the Endocrinology Department for suspected central hyperthyroidism. Her T3, free T4, TSH, and ACTH were elevated after Oregovomab administration, and her growth hormone was measured at >80 ng/mL. However, the brain MRI showed no pituitary adenoma, and it was confirmed that the false positives were due to heterophilic antibodies. Conclusion: Heterophilic antibodies have been recognized for a long time, but caution is needed as mouse-derived antibodies are still used in early-stage research. These antibodies can cross-react with non-homologous antigens, interfere with immunoassays, and lead to inaccurate test results. Presentation: Saturday, July 12, 2025