Introduction: Diffuse idiopathic pulmonary neuroendocrine hyperplasia (DIPNECH) is a rare condition that is likely underdiagnosed owing to the lack of established and validated diagnostic criteria. These clinical guidelines are empirical and created on the basis of a limited number of studies. This study was designed to validate the existing criteria and to identify new clinical parameters that can accurately diagnose DIPNECH. Methods: Patients with DIPNECH were identified from a cohort that underwent surgical lung resection for pulmonary carcinoids. The study cohort included a total of 105 consecutive cases with neuroendocrine lesions. Initial diagnostic predictors of DIPNECH were selected from the literature. We employed univariate and multivariate models to evaluate the association of clinical, pathologic, radiologic variables with the likelihood of DIPNECH. Results: Univariate analysis identified age, sex, chronic obstructive pulmonary disease diagnosis, obstructive abnormalities, pulmonary nodules, mosaicism, absolute numbers of pulmonary neuroendocrine lesions (PNELs), and the number of tumorlets as significant DIPNECH predictors (for p < 0.05). After adjustment for sampling variations, the ratio of the total number of PNELs to the number of bronchioles was found to be considerably higher in DIPNECH category. Multivariate analysis identified the total number of PNELs and multiple pulmonary nodules (>10) as independent predictors of DIPNECH. The performance of our criteria revealed an accuracy of 76% in detecting DIPNECH cases. Conclusions: We proposed a set of diagnostic criteria for DIPNECH on the basis of an expert-panel approach integrating pathological features, radiology, and clinical data. Our findings will help identify DIPNECH patients, without a pathological confirmation of a neuroendocrine lesion. Before the implementation of these criteria in clinical practice, they require further validation in multiinstitutional cohorts.

e21590 Background: Uveal melanoma (UM) is a rare subtype of melanoma. Real-world data is needed to guide management since patients with advanced UM were excluded from immune checkpoint inhibition (ICI) phase III clinical trials. Lymphopenia and elevated monocyte count, which represents a surrogate marker of systemic inflammation and a source of pro-angiogenic tumor-associated macrophages (TAM), have been associated with poor treatment outcomes in various solid tumors. We sought to characterize ICI efficacy in patients with UM vs cutaneous melanoma (CM) and to investigate pre-treatment lymphocyte-to-monocyte ratio (LMR) as a biomarker of response. Methods: We conducted a multicentric cohort study across 3 academic centers in Canada. Best overall responses as per the investigators were recorded. Overall survival (OS) and progression-free survival (PFS) were compared using the log rank (Mantel-Cox) test, with univariate analyses performed using Cox proportional hazard regression model. Results: A total of 122 patients with metastatic melanoma were included, either UM (n = 60) or CM (n = 62). UM patients were treated either with anti-PD-1 monotherapy (69%) or combination with anti-CTLA-4 (31%). Median OS was 35.4 months for CM versus 8.0 months for UM (HR 0.38, 95%CI 0.24-0.60, p = 0.0001). Median PFS was 10.7 months for CM versus 3.5 months for UM (HR 0.38, 95%CI 0.22-0.65, p = 0.0001). Best overall response in the UM group was progressive disease (74%), stable disease (10%) or partial response (16%). In UM patients, higher baseline LMR (HR 0.48, 95%CI 0.24-0.97, p = 0.04) and presence of immune-related adverse events (HR 0.42, 95%CI 0.20-0.89, p = 0.02) were associated with improved OS in univariate analysis. In CM, such association with high LMR was not significant (HR 0.58, 95% 0.28-1.21, p = 0.10) unless excluding patients with corticosteroid-induced lymphopenia due to recently treated brain metastases (HR 0.42, 95%CI 0.19-0.92, p = 0.03). Conclusions: Advanced UM treated with ICI have inferior survival outcomes compared with cutaneous primaries. Higher pre-treatment LMR is associated with improved OS to ICI in UM patients and could represent a surrogate marker of immune activation. Our findings reinforce the need for new treatment strategies in UM.