1516 Background : In the U.S, LGBTQ+ people face higher cancer rates and worse outcomes than the general population. Few studies have described the experiences of LGBTQ+ people and their caregivers during treatment. As part of an implementation science initiative aimed at improving care for LGBTQ+ patients, we conducted a large survey (n=817) to understand treatment experiences of this population. Here we report our findings which provide insight into how stigma and incorrect assumptions may contribute to medical mistrust and worse experiences. Methods: In 2023, 817 diverse LGBTQ+ cancer patients from academic and community-based settings, as well as patient advocacy groups, completed web-based surveys evaluating their care experiences during cancer treatment. Participants included patients with gastric (n=165), breast (n=238), ovarian (n=218), prostate (n=56), and colorectal cancers (n=140), including 83 gender non-conforming patients. Results: Most LGBTQ+ patients (80%) reported not receiving appropriate preventative cancer screening, with top barriers including provider did not mention cancer screening tests (40%) and did not have a healthcare provider (28%). Additionally, only 24% felt at least moderately comfortable disclosing their LGBTQ+ status. Inclusive measures that helped patients feel most comfortable included care teams sharing/displaying their own pronouns (39%), making public statements of support (43%), or wearing personal items indicating acceptance (39%). Of those who did disclose their identity, only 50% of gender-expansive patients reported consistently being referred to by the correct names and pronouns. Importantly, patients reported that only 34% of their partners/caregivers felt welcome at appointments, and only 4% felt respected by the care team. Few patients reported receiving key supportive care services, including counseling/support groups (23%), quality-of-life related care, such as sexual function counseling (23%), and LGBTQ-specific resources/education (19%). Furthermore, less than half of LGBTQ+ patients discussed with HCPs how cancer treatment affects fertility (41%), fertility preferences (26%), or fertility preservation (14%), even though only 22% of patients reported not being eligible for fertility services. Interestingly, many of these gaps in care differed based on cancer type. For example, prostate, colorectal, and gastric patients were more likely to report not feeling safe disclosing their LGBTQ+ status (80%, 69%, and 54% respectively), while breast cancer patients were more likely to report having discussed fertility prior to starting treatment (64%). Conclusions: This study offers insights into experiences of LGBTQ+ patients and confirms disparities in care are real and pervasive. Ongoing education and inclusion efforts can help create a safe and welcoming environment, enabling equitable care and improved outcomes.