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9583 Background: There is controversy regarding sentinel lymph node biopsy (SLNB) in clinically node-negative Merkel Cell Carcinoma (MCC). We compared MCC recurrence and survival between patients who did versus did not undergo a SLNB. Methods: Patients with MCC across 13 Canadian centers were reviewed, from 2000-2018. Of a total cohort of 750 patients, 485 had clinically node-negative disease at presentation. A propensity score was created. The association between SLNB and local, regional and distant recurrence, and cancer-specific and overall survival were evaluated using competing risks and Cox proportional hazards regression. Results: 195 patients (40.2%) underwent a SLNB. SLNB was performed more commonly in younger, healthier patients with MCC located in the extremities or torso (Table). The results of 177 SLNBs were available; 60 (33.9%) were positive. SLNB-positive patients underwent completion dissection (n=15, 25%), completion dissection and nodal radiation (n=22, 36.7%), nodal radiation alone (n=18, 30%) or observation (n=5, 8.3%). Patients who did not undergo a SLNB underwent nodal radiation alone (n=40, 13.8%) or observation (n=250, 86.2%). The median follow-up was 2.7 years (range 0.2-14.4). The regional recurrence rate was 14.5% (n=17) among SLNB-negative versus 15% (n=9) among SLNB-positive patients. Among patients who did not undergo a SLNB, the regional recurrence rate was 25.2% (n=63) among those who underwent observation and 15% (n=6) among those who received nodal radiation alone. After propensity score matching, SLNB patients had a lower risk of regional recurrence (sHR 0.54 95% CI 0.34-0.86 p=0.01) and improved overall survival (HR 0.32 95% CI 0.23-0.45 p<0.01), but there was no difference in local recurrence (sHR 0.92 95% CI 0.50-1.69 p=0.79), distant recurrence (sHR 0.88 95% CI 0.52-1.49 p=0.63), or cancer-specific survival (HR 0.67 95% CI 0.31-1.45 p=0.31). Conclusions: SLNB is associated with a reduced risk of regional recurrence and improved overall survival. The role of SLNB in selecting patients for emerging therapies, such as immunotherapy, needs to be evaluated. [Table: see text]

Background How well imaging size agrees with pathologic size of gastric gastrointestinal stromal tumors (GISTs) is unknown. GIST risk stratification is based on pathologic size, location, and mitotic rate. To inform decision making, the size discrepancy between imaging and pathology for gastric GISTs was investigated. Methods Imaging and pathology reports were reviewed for 113 patients. Bland–Altman analyses and intraclass correlation (ICC) assessed agreement of imaging and pathology. Changes in clinical risk category due to size discrepancy were identified. Results Computed tomography (CT) (n = 110) and endoscopic ultrasound (EUS) (n = 50) underestimated pathologic size for gastric GISTs by 0.42 cm, 95% confidence interval (CI): (0.11, 0.73), p = 0.008 and 0.54 cm, 95% CI: (0.25, 0.82), p < 0.001, respectively. ICCs were 0.94 and 0.88 for CT and EUS, respectively. For GISTs ≤ 3 cm, size underestimation was 0.24 cm for CT (n = 28), 95% CI: (0.01, 0.47), p = 0.039 and 0.56 cm for EUS (n = 26), 95% CI: (0.27, 0.84), p < 0.0001. ICCs were 0.72 and 0.55 for CT and EUS, respectively. Spearman's correlation was ≥0.84 for all groups. For GISTs ≤ 3 cm, 6/28 (21.4% p = 0.01) on CT and 7/26 (26.9% p = 0.005) on EUS upgraded risk category using pathologic size versus imaging size. No GISTs ≤ 3 cm downgraded risk categories. Size underestimation persisted for GISTs ≤ 2 cm on EUS (0.39 cm, 95% CI: [0.06, 0.72], p = 0.02, post hoc analysis). Conclusion Imaging, particularly EUS, underestimates gastric GIST size. Caution should be exercised using imaging alone to risk‐stratify gastric GISTs, and to decide between surveillance versus surgery.

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Caustic soda for the manufacture of a local variety of soap -the cause of untold suffering in the lives of children in a developing country. Mohammed Bukari,

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BackgroundWe hypothesized that there are geographic areas of increased cancer incidence in Alberta, and that these are associated with high densities of oil and gas(O+G) infrastructure. Our objective was to describe the relationship between O+G infrastructure and incidence of solid tumours on a population level.MethodsWe analyzed all patients &gt;=18 years old with urological, breast, upper GI, colorectal, head and neck, hepatobiliary, lung, melanoma, and prostate cancers identified from the Alberta Cancer Registry from 2004-2016. Locations of active and orphan O+G sites were obtained from the Alberta Energy Regulator and Orphan Well Association. Orphan sites have no entity responsible for their maintenance. ArcGIS (ESRI, Toronto, Ontario) was used to calculate the distribution of O+G sites in each census distribution area (DA). Patient residence at diagnosis was defined by postal code. Incidence of cancer per DA was calculated and standardized. Negative binomial regression was done on O+G site density as a categorical variable with cutoffs of 1 and 30 wells/100km2, compared to areas with 0 sites.Results125,316 patients were identified in the study timeframe;58,243 (46.5%) were female, mean age 65.6 years. Breast (22%) and prostate (19.8%) cancers were most common. Mortality was 36.5% after a median of 30 months follow up (IQR 8.4 – 68.4). For categorical density of active O+G sites, RR was 1.02 for 1-30 sites/100km2 (95% CI=0.95-1.11) and 1.15 for &gt;30 sites/100km2 (p&lt;0.0001, 95%CI=1.11-1.2). For orphan sites, 1-30 sites RR was 1.25 (p&lt;0.0001, 95%CI=1.16-1.36) and 1.01 (p=0.97, 95%CI=0.7-1.45) for &gt;30 sites. For all O+G sites, RR for 1-30 sites was 1.03 (p=0.4328, 95%CI=0.95-1.11) and 1.15 (p&lt;0.0001, 95%CI=1.11-1.2) for &gt;30 sites.ConclusionWe report a statistically significant correlation between O+G infrastructure density and solid tumour incidence in Alberta. To our knowledge this is the first population-level study to observe that active and orphan O+G sites are associated with increased risk of solid tumours. This finding may inform policy on remediation and cancer prevention.