Association of Race and CA 19-9 Nonproduction with Limited Pathologic Response to Neoadjuvant Chemotherapy in Patients with Localized Pancreatic Cancer.

609 Background: Black patients with pancreatic ductal adenocarcinoma (PDAC) are less likely to have major pathologic response (MPR) following induction chemotherapy compared to non-Black patients. Rare reports have suggested that Black patients are more likely to be CA 19-9 non-producers. We aimed to determine if disproportionate rates of CA 19-9 nonproduction underlie racial differences in neoadjuvant chemotherapy response in patients with localized PDAC. We also explored differences in somatic mutations between CA 19-9 producers (CAprod) and non-producers (CAnonprod). Methods: Black and White patients with localized PDAC receiving ≥ 2 cycles of neoadjuvant chemotherapy followed by pancreatectomy (2010-2019) at 7 high-volume centers were reviewed. Patients were categorized as CAprod (CA 19-9 > 5 U/mL) or CAnonprod (CA 19-9 ≤ 5 U/mL). Uni- and multi-variable models evaluated differences in rates of CAnonprod by race, and the association of CAnonprod with MPR (CAP 0/1). The Pancreatic Cancer Action Network (PanCAN)’s SPARK health data platform which contains clinical and multi-omic data from the PanCAN Know Your Tumor program was queried to identify patients with CA 19-9 and genomic data. Fisher’s exact test was used to compare differentially mutated genes between CAprod and CAnonprod patients. Results: Our cohort included 385 (93.3%) CAprod and 30 (6.7%) CAnonprod. CAnonprod patients were more likely to be Black than CAprod (50.0% vs 12.5%, p<0.01). There were no other differences in demographic or clinical features between CAnonprod and CAprod. Most patients received FOLFIRINOX vs Gemcitabine based chemotherapy (60.3% CAprod vs. 56.7% CAnonprod, p=0.27) with a median number of 4.0 vs 5.0 cycles (p=0.83), respectively. Rate of MPR was significantly higher in patients with CAprod compared with CAnonprod patients (26.3% vs 7.7%, p=0.03). No CAnonprod patient had a complete pathologic response vs 28 (7.3%) of CAprod (p=0.12). CAnonprod was independently associated with decreased odds of MPR (OR 0.21, CI [0.04-0.99]). Black race was independently associated with increased odds of CAnonprod (OR 8.66, CI [3.81 – 19.7]). When stratified by production of CA 19-9, there was no significant difference between rate of MPR between Black and White patients. In the PanCAN KYT analysis, CAnonproduc had higher rates of SWI/SNF alterations (50.0% of CAnonprod vs 30.1% of CAprod, P<0.01;P-adj=ns; ARID1B was the most frequently mutated SWI/SNF gene in CAnonprod (31.0% vs 9.0% CApos, p<0.01; P-adj=ns). Conclusions: CAnonprod were more likely to be Black and have significantly worse rates of MPR following neoadjuvant chemotherapy in patients with localized PDAC. Moreover, CAnonprod was associated with higher rates of SWI/SNF alterations, noting a potential biologic basis for racial differences in chemotherapy response to curative-intent treatment for PDAC.