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Introduction: Checkpoint inhibitors (CPI) have significantly improved survival among patients with various cancer types. Prior studies have shown a correlation between immune cell infiltration and poorly differentiated cancers. This study evaluated the impact of poorly differentiated histology on survival in patients with advanced gastrointestinal cancers treated with immunotherapy. Methods: This study was a retrospective, single-center analysis of patients with gastrointestinal cancers treated with CPIs between 2016 and 2021. Univariate and multivariable analyses were performed to identify factors associated with patient outcome. Kaplan-Meier analysis and Cox proportional hazards models were used to assess the association between tumor and patient characteristics, progression-free survival, and overall survival. Results: A total of 123 patients were eligible and included in the analysis. Median age was 66 years (23–88 years). Majority had stage IV disease (89%), were white (65.5%), and were male (64.5%). Most common diagnoses were hepatocellular carcinoma (30.5%), gastric adenocarcinoma (16.5%), esophageal adenocarcinoma (17%), and colorectal cancer (19.8%). About 32% of the tumors were microsatellite instability-high (MSI-High/dMMR), with BRAF V600E mutation rate of 10%. About 25% of the patients received CPIs as initial treatment, while 35.5% had received two or more prior lines of therapy. Compared with well and moderately differentiated histology, patients with poorly differentiated tumors had a shorter median overall survival (mOS) (not reached [NR] vs. NR vs. 9.3 months, p = 0.0264). There was no statistically significant difference in median progression-free survival (mPFS) between histology types (2.5 vs. 4.2 vs. 2 months, p = 0.1314). On univariate survival analysis, moderately differentiated tumors correlated with a significantly longer mOS (HR: 0.48, CI: 0.24–0.93, p = 0.030) and mPFS (HR: 0.62, 95% CI: 0.38–1.00, p = 0.048) compared to poorly differentiated histology. Female patients (HR: 0.55, 95% CI: 0.34–0.90, p = 0.018) and the Eastern Cooperative Oncology Group (ECOG) of 1 (vs. ≥2) had significantly longer mPFS (HR: 0.58, 95% CI: 0.35–0.97, p = 0.036). ECOG of 1 also correlated with longer mOS (HR: 0.47, 95% CI: 0.23–0.94, p = 0.034). Microsatellite stable (MSS) tumors had significantly shorter mPFS (HR: 5.74, 95% CI: 2.41–13.63, p < 0.001) and mOS (HR: 5.45, 95% CI: 1.64–18.12, p = 0.006). The number of prior systemic therapies was also associated with shorter mPFS (HR: 1.19, 95% CI: 1.03–1.39, p = 0.022) and mOS (HR: 1.23, 95% CI: 1.01–1.50, p = 0.045). On multivariable analyses, ECOG status of 0/1 versus ≥2 and MSI-High/dMMR versus MSS remained significantly associated with longer mPFS and mOS. There was no correlation with histologic differentiation status, race, or mutations such as BRAF V600E or KRAS. Conclusion: Results from this study demonstrate that poorly differentiated histology was associated with shorter mOS but was not associated with improved PFS in patients treated with CPI. Treatment-naïve patients, moderately differentiated tumors, female gender, ECOG 1, and MSI-High/dMMR were most likely to benefit from CPI.

Introduction: Fibrolamellar carcinoma (FLC) is a rare liver cancer that predominantly affects younger patients without a history of liver disease. Surgical resection is the cornerstone of therapy and represents the best potentially curative treatment option. Modest objective responses with cytotoxic chemotherapy alone or combined with immune checkpoint inhibitors (ICIs) have been reported; however, there are no established systemic therapy regimens for unresectable or metastatic FLC. Case Presentation: We report a case of a 23-year-old woman with FLC who presented with a 11.5 × 8.3 cm left liver mass and subsequently underwent resection as initial therapy. Molecular analysis of her surgical tissue revealed a DNAJB1-PRKACA fusion gene. The patient developed biopsy-proven recurrent FLC with multiple liver lesions but without any distant metastatic disease only 3 months after initial resection. In light of emerging data, the patient was treated with a novel triple therapy regimen including 5-fluorouracil (5-FU), interferon (IFN) alfa-2b, and nivolumab. Partial radiographic response was achieved after 4 treatments and complete response was achieved after 12 cycles with the combination. The patient received 2 more doses of 5-FU/IFN alfa-2b without nivolumab and underwent orthotopic liver transplantation (OLT) 6 months after the last dose of ICI. Pathological examination of the explanted liver remarkably confirmed pathologic complete response. She remains recurrence-free and is on active surveillance. Discussion/Conclusion: For patients with unresectable/recurrent FLC with no distant disease, the combination of 5-FU, IFN alfa-2b, and nivolumab could be an effective systemic therapy option. The use of this chemoimmunotherapy regimen to downstage FLC prior to OLT may be worth investigating further.