Immunohistochemistry of the nuclear mismatch repair (MMR) proteins MSH2, MSH6, MLH1, and PMS2. The presence of each protein is assessed by nuclear staining verified by pathologic analysis with (+) indicating present and (−) indicating absent staining. a, Displayed are two MMR-proficient tumoroids, RC-MSK-001 and RC-MSK-002. b, Displayed are two MMR-deficient tumors. RC-MSK-031 is deficient in MSH2 and MSH6. RC-MSK-034 is deficient in MLH1 and PMS2. Scale bars, 50 μm. All representative images are from one patient-specific tumor-to-tumoroid derivation.