Decoding the expression pattern of MUC3A in gastric adenocarcinoma: unveiling the key to successful immunotherapy

ABSTRACTAims Despite the promise of immunotherapy for gastric adenocarcinoma, resistance is common, necessitating the validation of new targets. Based on our previous bioinformatics analysis, the MUC3A antigen emerged as a promising candidate for immunotherapy against gastric adenocarcinoma. However, a comprehensive understanding of its expression at protein level remains elusive, despite its crucial role in determining clinical response. We also sought to establish a connection between the expression pattern and relevant clinical variables of the disease, whenever feasible.Methods Immunohistochemistry was used to determine the percentage of MUC3A-positive tumor cells in primary (PT) and metastatic tumor (MT) sites of 190 gastric adenocarcinoma patients. We also evaluated the association between MUC3A expression and variables such as Lauren classification, history of neoadjuvant chemotherapy and/or radiotherapy, and overall patient survival.Results Median MUC3A expression was 50% in PT and 70% in MT sites, exhibiting a positive correlation. MT intestinal type showed significantly higher MUC3A expression compared to other types. Neoadjuvant therapy history did not affect MUC3A expression. Higher MUC3A expression correlated with improved survival.Conclusions Based on our previous bioinformatics data and the consistently high expression of MUC3A on gastric tumor cells, we propose advancing experimental aspects of anti-MUC3A immunotherapy for gastric adenocarcinoma.KEYWORDS: Gastric adenocarcinomaMUC3Amucinantigenic targetsimmunotherapyDisclaimerAs a service to authors and researchers we are providing this version of an accepted manuscript (AM). Copyediting, typesetting, and review of the resulting proofs will be undertaken on this manuscript before final publication of the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal relate to these versions also. Article highlightsPrevious reports from clinical trials involving therapeutic agents in solid tumors have indicated that a minimum expression of 50% for antigenic targets is necessary to observe any clinical response.In our previous report, we bioinformatically emphasized the potential of MUC3A as a target for immunotherapy in gastric adenocarcinoma, albeit relying on transcriptomic data. Hence, it is reasonable to evaluate the protein expression of MUC3A on tumor cells (IHC approach) in order to make predictions about the efficacy of future immunotherapies.More than 50% of the patients exhibited MUC3A expression levels higher than 50 and 70 percent in PT and MT, respectively. The expression levels were significantly higher in the third and fourth quartiles of the samples, with the fourth quartile showing fluctuations between 85% and 100% in PT sites, and 90% to 100% in MT sites. Notably, there was a positive association between MUC3A expression in PT and MT sites, and higher MUC3A expression was correlated with higher survival rates.Based on our prior bioinformatics data suggesting the suitability of MUC3A for immunotherapy in gastric adenocarcinoma, coupled with recent findings showing consistent high expression of MUC3A on gastric tumor cells, we strongly encourage the scientific community to advance their exploration of the experimental aspects related to anti-MUC3A immunotherapy. Furthermore, the correlation between better survival rates and higher expression of MUC3A in gastric adenocarcinoma may support the concept that immunotherapy against MUC3A aligns with the patients’ native immune response.Declaration of InterestsThe authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.Reviewer disclosuresPeer reviewers on this manuscript have no relevant financial or other relationships to disclose.Authors’ contributionsMS, NS, and MN designed the study; MS and BS performed the IHC evaluations; RS performed the statistical data analyses; VM, VH, and MN prepared the manuscript.AcknowledgmentsWe deeply thank patients and their families who participated in this research with no expectations.Ethics approvalThis study was performed after the approval of Institutional Review Board of Tehran University of Medical Sciences (approval ID: IR.TUMS.DDRI.REC.1397.017).Consent to participateInformed consent was obtained from all patients at the time of surgery for the use of their paraffin-embedded tissue blocks in research after finalizing their diagnostic procedure.Availability of data and materialsAll the data analyzed in this study is included in this published manuscript.Supplementary materialSupplemental data for this article can be accessed online at https://doi.org/10.1080/14728222.2023.2293764Fig 1. Preparation of TMA slides. Based on a preceding H&E evaluation of tumor tissues with gastric adenocarcinoma, two cores were collected from each anatomical site, the PT and the MT sites, for subsequent MUC3A immunostaining and scoring. Following MUC3A immunostaining, the percentage of positively stained tumor cells was determined among all tumor cells in each core. Abbreviations in alphabetical order include FFPE: Formalin-fixed paraffin-embedded; H&E: Hematoxylin and eosin; IHC: Immunohistochemistry; MT: Metastatic tumor; MUC3A: mucin 3A, cell surface associated; PT: Primary tumor; TMA: Tissue microarray.Display full sizeFig 2. MUC3A IHC-based expression pattern in gastric adenocarcinoma a) a representative core stained for MUC3A and its corresponding isotype control, shown at different objective magnifications b) Box-and-whisker plot depicting MUC3A expression at PT and MT sites c) categorized for Lauren tumor classification d) previous history of neoadjuvant therapy e) and tumor stage. The multiplication sign in the boxes represents mean (average) of the data. Quartile values (Q1, Q2, and Q3) are indicated at the right side of the boxes. The number of patients in each group is shown below each bar. f) Correlation between MUC3A expression at PT and their corresponding MT sites. Abbreviations in alphabetical order include D: Diffuse type; I: Intestinal type; IHC: Immunohistochemistry; MT: Metastatic tumor; MUC3A: mucin 3A, cell surface associated; PT: Primary tumor; W: With a history of neoadjuvant therapy; W/O: Without a history of neoadjuvant therapy.Display full sizeFig 3. Kaplan-Meier survival curves of gastric cancer patients with above and below median MUC3A expression. a) PT and b) MT. Abbreviations in alphabetical order include MT: Metastatic tumor; MUC3A: mucin 3A, cell surface associated; PT: Primary tumor.Display full sizeAdditional informationFundingThis project was funded by Tehran University of Medical Sciences, Digestive Disease Research Institute (ID: 40230-37-03-97).