Potential Actionable Targets in Appendiceal Cancer Detected by Immunohistochemistry, Fluorescent in Situ Hybridization, and Mutational Analysis

Background: Appendiceal cancers are rare and consist of carcinoid, mucocele, pseudomyxoma peritonei (PMP), goblet cell carcinoma, lymphoma, and adenocarcinoma histologies. Current treatment involves surgical resection or debulking, but no standard exists for adjuvant chemotherapy or treatment for metastatic disease.

Methods: Samples were identified from approximately 60,000 global tumors analyzed at a referral molecular profiling CLIA-certified laboratory. A total of 588 samples with appendix primary tumor sites were identified (male/female ratio of 2:3; mean age =55). Sixty-two percent of samples were adenocarcinomas (used for analysis); the rest consisted of 9% goblet cell, 15% mucinous; 6% pseudomyxoma, and less than 5% carcinoids and 2% neuroendocrine. Tests included sequencing [Sanger, next generation sequencing (NGS)], protein expression/immunohistochemistry (IHC), and gene amplification [fluorescent in situ hybridization (FISH) or CISH].

Results: Profiling across all appendiceal cancer histological subtypes for IHC revealed: 97% BRCP, 81% MRP1, 81% COX-2, 71% MGMT, 56% TOPO1, 5% PTEN, 52% EGFR, 40% ERCC1, 38% SPARC, 35% PDGFR, 35% TOPO2A, 25% RRM1, 21% TS, 16% cKIT, and 12% for TLE3. NGS revealed mutations in the following genes: 50.4% , 21.9% , 17.6% , 16.5% , 10% , 7.5% , 5.5% , 5.0% , and 1.8% .

Conclusions: Appendiceal cancers show considerable heterogeneity with high levels of drug resistance proteins (BCRP and MRP1), which highlight the difficulty in treating these tumors and suggest an individualized approach to treatment. The incidence of low TS (79%) could be used as a backbone of therapy (using inhibitors such as 5FU/capecitabine or newer agents). Therapeutic options includeTOPO1 inhibitors (irinotecan/topotecan), EGFR inhibitors (erlotinib, cetuximab), PDGFR antagonists (regorafenib, axitinib), MGMT (temozolomide). Clinical trials targeting pathways involving and may be also considered. Overall, appendiceal cancers have similar patterns in their molecular profile to pancreatic cancers (can we say this, any statistical analysis done?) and have differential expression from colorectal cancers. These findings indicate the need to evaluate patient samples for patterns in marker expression and alteration, in order to better understand the molecular biology and formulate a personalized therapy approach in these difficult to treat cancers (supported by a grant from Caris Life Sciences).