Berrino Enrico, Aquilano Maria Costanza, Valtorta Emanuele, Amodio Vito, Germano Giovanni, Gusmini Marco, Gizzi Katiuscia, Fenocchio Elisabetta, Sapino Anna, Marsoni Silvia, Sartore-Bianchi Andrea, Bardelli Alberto, Siena Salvatore, Bonoldi Emanuela, Marchiò Caterina
Candiolo Cancer Institute, FPO-IRCCS, Candiolo, Italy; Department of Medical Sciences, University of Turin, Turin, Italy.
Niguarda Cancer Center, Grande Ospedale Metropolitano Niguarda, Milano, Italy.
Mod Pathol. 2023 Feb;36(2):100012. doi: 10.1016/j.modpat.2022.100012. Epub 2023 Jan 10.
Mismatch repair (MMR) protein expression in colorectal cancer (CRC) cells is usually homogeneously retained or lost. Rare lesions may show a heterogeneous pattern of MMR protein expression. We evaluated MMR protein expression (MLH1, MSH2, MSH6, and PMS2) in 200 CRCs, identifying 3 groups with proficient MMR protein expression (MMRp), deficient MMR protein expression (MMRd), and heterogeneous MMR protein expression (MMRh). MMRh tumors were microdissected on the basis of the expression of the heterogeneous marker. DNA was extracted and subjected to targeted sequencing. RNA was purified from bulk tumors of all MMRh cases and in a control series of 15 MMRp and 10 MMRd CRCs and analyzed using the PanCancer IO 360 Panel (NanoString Technologies). Twenty-nine of the 200 cases (14.5%) were MMRd. Nine cases (4.5%) showed a heterogeneous pattern of MMR expression, with 6 tumors harboring concomitant loss of one of the other MMR proteins, thus featuring areas with double loss at immunohistochemistry (IHC) testing (MMRh double-loss cases). Four of the 6 MMRh double-loss cases were suitable for a separate sequence variant analysis of IHC double-negative and IHC single-negative components of the tumor. In all lesions, both components exhibited a high tumor mutation burden (TMB). Nevertheless, a significant increase in TMB in the double-negative components was observed (mean TMB: negative, 70 mut/Mb vs positive, 59 mut/Mb) because of a higher number of subclonal variants compared with the other component. Comparative gene expression analyses among MMRd, MMRp, and MMRh CRCs highlighted differential gene expression patterns and an increased number of tumor-infiltrating lymphocytes in MMRh lesions, which is also characterized by a substantial population of exhausted CD8 lymphocytes. We describe a unique subgroup of CRCs showing heterogeneous expression of MMR proteins in a background of concomitant loss of one of the other markers.
错配修复（MMR）蛋白在结直肠癌（CRC）细胞中的表达通常是均匀保留或缺失的。罕见病变可能呈现MMR蛋白表达的异质性模式。我们评估了200例CRC中MMR蛋白（MLH1、MSH2、MSH6和PMS2）的表达，确定了3组，分别为MMR蛋白表达 proficient（MMRp）、MMR蛋白表达 deficient（MMRd）和MMR蛋白表达 heterogeneous（MMRh）。根据异质性标志物的表达对MMRh肿瘤进行显微切割。提取DNA并进行靶向测序。从所有MMRh病例的整块肿瘤以及15例MMRp和10例MMRd CRC的对照系列中纯化RNA，并使用泛癌IO 360 Panel（NanoString Technologies）进行分析。200例病例中有29例（14.5%）为MMRd。9例（4.5%）呈现MMR表达的异质性模式，其中6个肿瘤伴有其他MMR蛋白之一的同时缺失，因此在免疫组织化学（IHC）检测中表现为双缺失区域（MMRh双缺失病例）。6例MMRh双缺失病例中的4例适合对肿瘤的IHC双阴性和IHC单阴性成分进行单独的序列变异分析。在所有病变中，两个成分均表现出高肿瘤突变负荷（TMB）。然而，由于与另一个成分相比亚克隆变异数量更多，双阴性成分中的TMB显著增加（平均TMB：阴性，70个突变/Mb vs阳性，59个突变/Mb）。MMRd、MMRp和MMRh CRC之间的比较基因表达分析突出了差异基因表达模式以及MMRh病变中肿瘤浸润淋巴细胞数量的增加，MMRh病变的特征还包括大量耗竭的CD8淋巴细胞。我们描述了一组独特的CRC亚组，其在其他标志物之一同时缺失的背景下表现出MMR蛋白的异质性表达。
