12459 Exceptional Response To A Single Dose Of Pembrolizumab As Salvage Therapy In A Patient With Metastatic Adrenocortical Carcinoma (ACC)

Abstract Disclosure: L. Branchaud-Croisetière: None. J. Castilloux: None. E. Turcotte: None. A. Bégin: None. M. St-Jean: Advisory Board Member; Self; GlaxoSmithKline, HRA Pharmaceuticals. Research Investigator; Self; AstraZeneca, Novo Nordisk, Spruce Biosciences. Speaker; Self; GlaxoSmithKline, Recordati Rare Diseases. In advanced ACC, limited effective treatment options are available beyond mitotane and cytotoxic chemotherapy. PD-L1 blockade has shown promising results in small numbers of advanced ACC. In ACC, the reported partial response rate to pembrolizumab is around 25%.1 Only one case of a significant partial response to a single dose of Pembrolizumab as salvage therapy for metastatic ACC was previously published.1 In April 2023, a 19-year-old woman presented with severe hypertension, hypokalemia and clinical signs of Cushing syndrome (CS). Thoraco-abdominal scan revealed a left-sided cluster of confluent adrenal masses (7.3 x 14.4 x 11.4 cm), a left cortical renal lesion (2.8x2x2.1cm), a right ovarian teratoma (7.9 x 7.8x7.9 cm) and at least 25 pulmonary micronodules. FDG-PET SCAN revealed a significant hypermetabolism of the left adrenal lesions (SUV 18.6), ovarian teratoma (SUV 5.5) and pulmonary micronodules (SUV 1.1-2). Cortisol and androgens secretion was confirmed biochemically. Initially, she was not candidate for a debulking surgery because the tumor was surrounding the aorta, and mesenteric arteries. Hypertension and hypokalemia were treated with spironolactone, amlodipine, amiloride and irbesartan. Cushing syndrome was treated with metyrapone. In April 2023, Etoposide-Doxorubicine-Cisplatin (EDP) was administered in combination with Mitotane (max: 8g/day). After 6 cycles of EDP-M the disease regressed slightly but was considered stable based on RECIST criteria. After 8 cycles, the follow-up imaging showed a progression of the adrenal lesion (9.2x18.2cm) but stable pulmonary micronodules. A biopsy of the adrenal lesion, for therapeutic purpose, revealed microsatellite stability (MSS). The patient refused germinal genetic testing. It was decided in multidisciplinary tumor board to try Pembrolizumab. In December 2023, she received one cycle of Pembrolizumab (140mg), but the treatment was complicated by grade 4 immune-mediated hepatitis. A few weeks following Pembrolizumab she completely normalized her blood pressure and hypokalemia despite cessation of all her anti-hypertensive drugs. Pembrolizumab and Mitotane were stopped and hepatitis completely resolved after two months of Mycophenolate Mofetil and ongoing decreasing dose of prednisone. In March 2024, CT scan showed a 60% regression of the adrenal mass (4.1 x 7.2 cm), stability of the renal lesion and ovarian teratoma and complete resolution of the pulmonary micronodules. We suspect an ongoing effect of immunotherapy and Mitotane, since Mitotane levels were still in the therapeutic range (15.1 mg/L) six weeks following cessation. Mitotane was resumed in March 2024. The patient will potentially have a resection of the left adrenal lesion in the next month. This is second published case of a significant response to Pembrolizumab as second-line therapy for advanced ACC. 1 Raj Net al. J Clin Oncol. 2020 Presentation: 6/1/2024