Among patients with rectal cancer who achieve a complete clinical response (cCR) after neoadjuvant therapy and undergo nonoperative management (NOM), a subset experience tumor regrowth and require salvage surgery. We sought to identify clinicopathologic factors associated with tumor regrowth to assist in patient selection for NOM. Patients treated for rectal cancer at a single National Cancer Institute (NCI)-designated Comprehensive Cancer Center in whom NOM was pursued based on cCR or near-cCR were identified. Patients were stratified based on whether they developed tumor regrowth during follow-up. Tumor and treatment details were compared to identify factors affecting regrowth-free survival (RFS). Among 125 patients, 26 (20.8

Mutation in the gene Polymerase Epsilon (POLE) mutation has been associated with a hypermutant phenotype, improved prognosis, and more recently, investigated as a predictive biomarker for immunotherapy response 1 Rousseau B. Bieche I. Pasmant E. et al. PD-1 Blockade in Solid Tumors with Defects in Polymerase Epsilon. Cancer Discov. 2022; 12: 1435-1448 Crossref PubMed Scopus (27) Google Scholar . However, there is currently ongoing confusion in the oncology community regarding which specific POLE mutations drive the hypermutant phenotype and immune response, with some authors arguing that this applies to all nonsynonymous mutations in the coding regions of POLE2 Wang F. Zhao Q. Wang Y.N. et al. Evaluation of POLE and POLD1 Mutations as Biomarkers for Immunotherapy Outcomes Across Multiple Cancer Types. JAMA Oncol. 2019; 5: 1504-1506 Crossref PubMed Scopus (277) Google Scholar . POLE is a unique DNA polymerase that in addition to its primary function as a polymerase also has the ability to proofread and remove mismatched base pairs via an exonuclease domain. Selective loss-of-proofreading (LOP) function leads to error prone synthesis which drives elevated Tumor Mutational Burden (TMB) with a characteristic mutational signature 3 Hodel K.P. Sun M.J.S. Ungerleider N. et al. POLE Mutation Spectra Are Shaped by the Mutant Allele Identity, Its Abundance, and Mismatch Repair Status. Mol Cell. 2020; 78 (e1166): 1166-1177 Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar . Here we sought to end the controversy regarding which specific POLE mutant alleles predict response to immune therapy by generating for the first time a comprehensive list of POLE mutant alleles causing selective loss-of-proofreading (LOP) function.

Appendiceal adenocarcinoma (AA) represents a rare malignancy with a unique natural history characterized by peritoneal metastases without (except in rare instances) hematogenous spread. Despite this unique biology, it has historically been treated as an extension of colorectal adenocarcinoma (CRC). Given the growing data that chemotherapy designed for CRC is ineffective for many patients with AA, it is critical to understand the unique genomic landscape of AA. Patients with AA (N=855) undergoing circulating tumor DNA monitoring using SignateraTM Molecular Residual Disease Test were included. Whole exome sequencing (WES) of tumor tissue and matched normal were used to identify patient-specific somatic mutations. Tumor mutational burden (TMB) and Microsatellite Instability (MSI) were analyzed. Gene ontology (GO) and KEGG network analysis were applied to identify significantly dysregulated canonical pathways. As a comparison group, colon (N=900) and rectal (N=900) cancer cases were analyzed. The stage distribution for patients with AA was 50 (5.8%)/ 234 (27.4%)/ 164 (19.2%)/ 347 (40.6%)/ 60 (7.0%) for stage I/II/III/IV/unreported, respectively. A total of 1,091,024 variants were identified from the WES analysis of 855 tumor tissues, with a median of 47 variants per tumor. The vast majority of the variants were single nucleotide polymorphisms (SNPs) with rare insertions and deletions. AA had low TMB (median: 2.14 Muts/Mb) compared to rectal and colon (median: 3.61, 4.61 Muts/Mb, respectively) cohorts. Only 1.3% (11/855) of the AA tumors were MSI-High, significantly less frequent than in rectal (3.1%) and colon cancers (19.1%). The top five mutated genes in AA were KRAS (393, 45.9%), GNAS (209, 24.4%), TP53 (203, 24.2%), SMAD4 (108, 12.6%), and APC (80, 9.3%). Significant co-occurrence was observed for mutations, pairwise, KRAS-GNAS, KRAS-TP53, and SMAD4-TP53 (ORs 12.2, 3.5, 3.6, respectively, all q 40 single nucleotide variants demonstrated similarity to colon and rectal cohorts, despite the differences in mutation frequency of specific genes. Clock-like Signatures (SBS1 and SBS5) were observed in 413 cases (73.1%), followed by the Signatures of Mismatch Repair deficiency (SIG-MMR, SBS6 or SBS15) in 126 cases (22.3%). SIG-MMR tumors displayed significantly higher TMB (median 5.7 Muts/Mb, p < 0.001) and higher prevalence of MSI (8.7%) relative to tumors with Clock-like Signature. This study represents the largest WES analysis to date of AA tumors. Importantly, while there are overlapping mutational signatures, suggesting similarity in the mutagenic process with CRC, distinct mutational differences between AA and CRC were noted.

Appendiceal adenocarcinoma (AA) is a rare and heterogenous cancer with marked differences in clinical course between high- and low-grade tumors. Unlike colorectal cancer (CRC) and other gastrointestinal malignancies, AA virtually never has hematogenous metastases, rather, metastasis is limited to the peritoneum. Here we present a retrospective, single institution study of AA to identify the prevalence of detectable ctDNA, evaluate the predictive value of positive ctDNA, and assess what clinical, pathologic, or molecular features predict positive ctDNA. 69 blood samples from 63 patients with AA metastatic to the peritoneum were profiled with a CLIA approved 73 gene mutational panel (Guardant 360) as part of routine clinical practice. Paired tumor sequencing was available for 23 patients to allow for concordance testing. Out of 69 ctDNA samples, 43 were taken in the setting of radiographically apparent metastatic disease. Of these only 12 (27.9%) had any detectable mutation while 31 (72.1%) had no detectable ctDNA. High-grade tumors were more likely to have measurable ctDNA with detection rates of 3/16 (18.7%), 4/15 (26.7%), and 5/12 (41.7%) for well, moderately, and poorly-differentiated tumors, respectively. Detectable ctDNA was associated with worse overall survival (29.4 months for positive ctDNA vs not yet reached for negative ctDNA, HR = 4.7, p = 0.02), although not powered for subgroup analysis this association appeared to hold for both low- and high- grade tumors (HR 4.4, 2.8 respectively). Restricting analysis to the 23 patients with paired tissue and blood samples and 72 genes sequenced in both, of 44 mutations detected in tumor only 3 (GNAS, KRAS and TP53) were detected in blood (sensitivity of 6.8%). Six mutations (BRCA1, KIT, KRAS and TP53) were seen in blood but not tissue, which may represent either clonal hematopoiesis or somatic mutations missed in tissue sequencing. Overall, the sensitivity of ctDNA detection in metastatic AA was markedly less than what was observed in a cohort of 274 metastatic CRC patients from the same institution (288/581 = 49.6%). 26 AA patients with No Evidence of Disease (NED) clinically or radiographically after complete cytoreduction had ctDNA testing done. Of the 26, 7 had positive ctDNA (26.9%), while 19 were negative (73%). High-grade tumors were somewhat more likely to have detectable ctDNA with detection rates of 2/12 (16.7%), 2/9 (22.2%) and 3/7 (43%) for well, moderately, and poorly-differentiated tumors, respectively. Detectable ctDNA was a risk factor for recurrence (5/7, 71.4% detectable ctDNA vs. 5/19, 26.3% undetectable, HR = 4.5, p = 0.007). Restricting to high-grade patients, the three with detectable ctDNA had markedly shorter median duration to recurrence (4.0 vs. 26.9 months, HR = 3.8, p = 0.13). Sensitivity of ctDNA detection in metastatic AA is overall markedly lower than other metastatic gastrointestinal tumors, with detection more likely in high-grade tumors relative to low-grade. The presence of detectable ctDNA is associated with worse survival and increased risk of relapse in NED patients. The development of more sensitive ctDNA assays may improve ctDNA detection in AA.