Abstract Breast Cancer is the most frequently diagnosed cancer among women. Despite the decreasing death-rate, a large portion of patients experience long-term side effects. One of the most common is “chemobrain”: a series of subtle but persistent cognitive deficits that affect attention, memory, and speed of processing. There is a lack of consensus regarding the exact rate of “chemobrain” incidence(from 12% to 86% of patients complaining cognitive sequelae after adjuvant-therapies) primarily due to the heterogeneity of assessment measures used to quantify it. Our first aim was to estimate the prevalence of perceived cognitive deficits in breast cancer-survivors, and to address the relevance of psycho-social factors that might affect perceived cognitive functioning. The second aim was to better understand the specific impact on patients comparing possible differences in perceived cognitive functioning between a cohort of breast cancer-survivors and an age-matched group of women without oncologic diagnosis. A total of 216 subjects submitted an anonymous online questionnaire that included FACTCog v.3and 41 items investigating clinical history, cognitive reserve, sleep quality, dietary and health habits. Inclusion criteria were being female, aged between 25 and 75, lack of known psychiatric or neurological diseases. The study was approved by the Ethical Committee of University of Trieste. The study sample comprised 90 oncological patients, recruited through clinical oncology practices between Trieste - ASU GI and Cremona - ASST Breast Cancer Units, and 126 age-matched controls enrolled through LILT (Lega Italiana Lotta Tumori) - Trieste (Italy). To perform within and between groups comparisons, both populations (Breast-cancer patients’ and age-matched controls’) were subdivided in two subgroups each, based on FACTCog PCI18 score according to Van Dyk et al.(2020), cutpoints: Subjective Cognitive Complaints - SCC (PCI18<54) and No Subjective Cognitive Complaints - NSCC (PCI18 ≥54).Statistical analysis revealed that 36% of breast-cancer patients reported perceived cognitive deficits, while only for 18% of the age-matched control group this was the case (p<.001). We found a significant difference in perceived cognitive abilities (CogPCA p<.001), quality of life (CogQOL p<.001) and frequency of aerobic activity (moderate physical activity p<.01) between SCC versus NSCC patients with the former group showing worse scores in all reported measures. Between group analysis performed on breast-cancer group versus age-matched control group revealed a significant interaction of oncological diagnosis and SCC on measures of perceived cognitive abilities (CogPCA p<.001) and quality of life (CogQOL p<.001), indicating that SCC patients had worse scores on these measures. On the other hand, NSCC patients had higher scores on measures regarding how others (e.g., family members or close friends) perceived their cognitive abilities (p<.05).A significant effect of oncological diagnosis but not of SCC (or interaction between the two) was found on measures concerning sleep (Sleep quality index p<.05), indicating a strong effect of cancer diagnosis on sleep quality. Conversely when comparing the effect of cancer diagnosis on measures of physical activity no significant effect was found, instead a strong effect of SCC emerged (Physical activity index p<.01). Subjective perceived cognitive deficit affects the quality of life of breast cancer survivors, thus suggesting the usefulness of specific educational interventions to prevent stress-related effects. Citation Format: Thomas West, Bruna Scaggiante, Rita Ceccherini, Silva Foladore, Daniele Generali, Francesco Versace, Corrado Cavallero. The relevance of chemobrain in breast cancer survivors: An Italian exploratory study to measure incidence and psycho-social impact [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-10-12.