SAT-475 New Breast Cancer Therapy Atezolizumab, Leads to Thyroiditis

Background: A NSABP B 59 trial is currently underway to check the efficacy of an experimental drug, Atezolizumab (Anti-PDL 1 monoclonal antibody) in the treatment of triple negative breast cancer. In the trail, the drug is added to the usual neoadjuvant chemotherapy given before surgery and prolonged treatment with it is continued after surgery to reduce the recurrence. Listed adverse effects are immune medicated hyperthyroidism in 2% of population. Clinical Case: 32 y old Asian woman was diagnosed with triple negative left breast cancer in May 2018. She was started on paclitaxel, carboplatin and study medication Atezolizumab/Placebo in June 2018 and she received 4 cycles of the same and then it was stopped in August 2018. She was started back on the same in September 2018 which ended in November 2018. Patient tested positive for BRCA1 gene mutation and underwent bilateral mastectomy in December 2018. The study medication was restarted in January 2019. Patient is received a total of 11 doses of study medication and was due to receive 16 doses if she had finished the trial in June 2019. Patient received radiation therapy starting in January 2019 till February 2019. On her oncology visit in April 2019 patient was found to have a suppressed TSH of 0.009 with a high free thyroxine of 1.72 and an elevated free T3 of 5.4. She was referred to endocrinology for evaluation of thyroid abnormalities, as the study medication can cause thyroid problems. She denied symptoms of hyperthyroidism. TPO, TSI and anti-thyroglobulin antibodies were negative. Thyroid uptake scan showed uniformly decreased tracer distribution in both thyroid lobes consistent with thyroiditis. As per the protocol for the study medication as well as recommendations by the American Society of oncology, we waited for normalization of the thyroid function test before resuming the study medication. In July 2019, TSH normalized to 2.99 and free T4 0.97. She was noted to have low random cortisol level of 3.27 at 1000AM. ACTH stimulation test was performed and she responded appropriately. Hence could not take the remainder of the study medication that were scheduled until June 2019. She is on observation phase since June 2019 and currently doing well.