Relationship of microsatellite instability to mismatch repair deficiency in malignant tumors of dogs

Abstract

Background: Microsatellite instability (MSI) is a type of genomic instability caused by mismatch repair deficiency (dMMR) in tumors. Studies on dMMR/MSI are limited, and the relationship between dMMR and MSI is unknown in tumors of dogs.Objectives: We aimed to identify the frequency of dMMR/MSI by tumor type and evaluate the relationship between dMMR and MSI in tumors of dogs.Animals: In total, 101 dogs with 11 types of malignant tumors were included.Methods: We extracted DNA from fresh normal and tumor tissues. Twelve microsatellite loci from both normal and tumor DNA were amplified by PCR and detected by capillary electrophoresis. Each microsatellite (MS) was defined as MSI if a difference in product size between the tumor and normal DNA was detected. The dMMR was evaluated by immunohistochemistry with formalin-fixed paraffin-embedded tumor tissues. Next, we confirmed whether dMMR induces MSI by serial passaging of MMR gene knockout cell lines for 3 months.

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“…Therefore, further investigation using TILs will be required to confirm the suitability of this phenomenon as a treatment-response biomarker. Recent veterinary studies established the evaluation methods of MSI-H/dMMR and IHC of PD-L1 expression [ 4 16 ]. Hence, clinical trials incorporating more dogs with each tumor type are needed using those methods to develop a predictive biomarker for treatment-response, such as human studies [ 24 ].…”

“…No tumor tissue samples post-treatment were obtained from other cases. According to our previous reports [ 16 17 ], tissue sections (5-μm) were subjected to antigen retrieval by incubation in a citric acid buffer (pH 6.0) using a pressure cooker (Dako Japan, Tokyo, Japan). The sections were incubated with 3% of hydrogen peroxide in phosphate-buffered saline (PBS) to block endogenous peroxidase activity.…”