Although we did not find significant differences between previously concussed and non-concussed athletes in either the knowledge or the attitude questions as measured by their total scores, this study showed a high level of awareness of concussion in youth soccer players, while still highlighting a need for education. Limited distinctions were made among subgroups of players, suggesting directions of future research in investigating the role that outside factors may have on knowledge and perception of concussion.

Dear Editor, Delayed immunologic reactions have been described in association with the novel mRNA COVID-19 vaccines. We report the case of a 40-yearold male who presented with widespread pruritic urticarial indurated papules and plaques on the arms, legs, palms, and face 9 days following his first Moderna vaccination (Figure 1A,B). He denied constitutional

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Reflectance confocal microscopy (RCM) presents a non-invasive method to image actinic keratosis (AK) at a cellular level. However, RCM criteria for AK response monitoring vary across studies and a universal, standardized approach is lacking. We aimed to identify reliable AK response criteria and to compare the clinical and RCM evaluation of responses across AK severity grades. Twenty patients were included and randomized to receive either cryotherapy (n = 10) or PDT (n = 10). Clinical assessment and RCM evaluation of 12 criteria were performed in AK lesions and photodamaged skin at baseline, 3 and 6 months. We identified the RCM criteria that reliably characterize AK at baseline and display significant reduction following treatment. Those with the highest baseline odds ratio (OR), good interobserver agreement, and most significant change over time were atypical honeycomb pattern (OR: 12.7, CI: 5.7–28.1), hyperkeratosis (OR: 13.6, CI: 5.3–34.9), stratum corneum disruption (OR: 7.8, CI: 3.5–17.3), and disarranged epidermal pattern (OR: 6.5, CI: 2.9–14.8). Clinical evaluation demonstrated a significant treatment response without relapse. However, in grade 2 AK, 10/12 RCM parameters increased from 3 to 6 months, which suggested early subclinical recurrence detection by RCM. Incorporating standardized RCM protocols for the assessment of AK may enable a more meaningful comparison across clinical trials, while allowing for the early detection of relapses and evaluation of biological responses to therapy over time.

e21519 Background: Anti-PD-1 therapy has become a mainstay of advanced melanoma treatment. However, associated irAEs are common and contribute to significant delays or cessation of treatment. In this retrospective cohort study, we aim to characterize the real-world irAE profile of pembrolizumab at our institution and its prognostic implications. Methods: We evaluated unresectable stage III-IV melanoma patients treated with pembrolizumab between 2011 and 2016 at the University of Arizona Cancer Center (UACC). Information regarding demographics, treatment, irAEs, and hospitalizations were recorded. Adverse events were graded using the common terminology criteria for adverse events v.4.0 (CTCAE). Results: Seventy-three patients were identified, 4 (5.5%) with unresectable stage III and 69 (94.5%) with stage IV melanoma. The median age was 68; 48 (65.8%) patients were male and 25 (34.2%) were female. Nineteen patients (26.0%) had a preexisting autoimmune disorder. 171 irAEs were identified in 58 of the patients. 141 (82.5%) were Grade 1, 24 (14.0%) were Grade 2, and 6 (3.5%) were Grade 3. Incidence and time to onset of significant events is displayed in Table. Eleven (15%) patients were hospitalized, and 8 patients (11.0%) stopped treatment due to an irAE. Sixteen (84.2%) patients with a preexisting autoimmune condition experienced an irAE versus 78% of patients without an autoimmune condition. Twelve patients (75%) had an exacerbation of their autoimmune condition. Response could be assessed in 67 patients . 30 patients of the 67 (45%) had a CR or a PR and 37 patients (55%) had progressive disease (PD). 58 of 67 (87%) experienced an irAE. 29 (50%) of the 58 irAE patients had PD, while 8 (88.9%) of the 9 non-irAE patients had PD. The relative risk of progression in patients who experienced an irAE versus who did not was 0.56 (95% CI: 0.39-0.79, p= 0.001). Conclusions: Experience with pembrolizumab at our institution suggests a similar irAE profile compared to landmark trials, though we observed a higher percentage of patients who required discontinuation of pembrolizumab (11% versus 5% in Phase III trials). In our retrospective study, the risk for progression was significantly higher in patients without irAE versus with any irAE, suggesting that development of irAE could be a positive prognostic sign.[Table: see text]