Abstract Immune related adverse events (irAEs) from immune checkpoint inhibitors (ICIs) are well documented for nearly every organ system, except for the reproductive system. Mouse models have demonstrated that ICIs can decrease ovarian follicular reserve and impair oocyte maturation, which may have implications for fertility (PMID: 36008687). There are no studies investigating the effect of ICIs on fertility in humans. We sought to evaluate ovarian function in women treated with ICIs compared to untreated women by evaluating non-invasive surrogate markers of ovarian reserve, anti-müllerian hormone (AMH) and antral follicle counts (AFC). We enrolled women 18 - 40 years old diagnosed with stage III or IV melanoma. Participants underwent phlebotomy for AMH levels and a pelvic ultrasound to assess AFC. The medical record was retrospectively reviewed to obtain data on patient characteristics, treatments, and outcomes. A total of 14 patients with stage IIIA - IV melanoma participated. Six patients received ICI treatment before AMH and AFC testing while 8 had no prior ICI exposure. The ICI group ages ranged from 22-40 years with a median age of 31 years. The untreated group ages ranged from 25-39 years with a median age of 32 years. The time between starting an ICI and enrolling in the study ranged from 28 - 351 days. ICI regimens included ipilimumab/nivolumab, nivolumab, pembrolizumab, and atezolizumab (on a clinical trial). Four of these six patients experienced an irAE during their course, including: dermatitis, hepatitis, colitis, thyroid dysfunction, and adrenal insufficiency. Median AMH levels were lower for patients treated with ICIs (2.9 vs 4.0 ng/mL), as was median AFC (22.5 vs 23.5 ng/mL). Only three patients’ clinicians discussed fertility preservation. None of the patients underwent fertility preservation. Our study found lower AMH and AFC in women with melanoma who were treated with an ICI compared to untreated women. Although AMH and AFC are surrogate markers for ovarian reserve and fertility, and our study is a small cohort, these early results suggest that ICIs may impact ovarian function. Age is less likely to be a confounding factor as the median age of the treated group was younger than the untreated group. While these results are preliminary, when considered in conjunction with recent pre-clinical data showing changes within the ovaries after ICI treatment, fertility consultation should be considered for young women prior to ICI initiation. We are investigating associations between AMH, AFC, age, ICI exposure, and future pregnancies in an ongoing prospective study. Citation Format: Ashley Hickman, Katherine Smith, Zaraq Khan, Elizabeth Ann Enninga, Yulian Zhao, Elizabeth Cathcart-Rake, Haidong Dong, Lisa Kottschade, Svetomir Markovic, Heather Montane, Anastasios Dimou, Yiyi Yan. Investigating the effect of immune checkpoint inhibitors (ICI) on ovarian function in young patients with melanoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6644.