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    Topic review

    Instability of Non-Standard Microsatellites

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    Submitted by: Luigi Pasini


    Elevated microsatellite alterations at selected tetranucleotide (EMAST) repeats are a genetic signature of colorectal cancers and are caused by somatic dysfunction of the DNA mismatch repair (MMR) protein MutS Homolog 3 (MSH3). There are very few data showing the relation of EMAST presence in the genome with the response to treatment, and there is no information about the metastatic setting. To the best of our knowledge, this is the first study evaluating the correlation between EMAST and response to treatment with chemotherapy or chemotherapy plus bevacizumab in metastatic colorectal cancer (mCRC).


    1. Introduction

    Although metastatic colorectal cancer (mCRC) is the third cause of cancer-related deaths worldwide [1][2], the last two decades have seen the introduction of new cytotoxic and biological agents that have improved treatment and overall survival (OS) [3], aided by a better understanding of the molecular mechanisms of the disease and the identification of new prognostic and predictive markers. The introduction of targeted therapies for mCRC, such as the anti-epidermal growth factor receptor (EGFR) monoclonal antibodies cetuximab and panitumumab, or the anti-vascular endothelial growth factor (VEGF-A) bevacizumab (B), has represented an important breakthrough in this setting, but there are still no validated predictive biomarkers for anti-angiogenic treatment [4].

    Genomic instability is a landmark of mCRC and is the main effector that leads to the accumulation of mutations in repeated DNA sequences. Microsatellite instability (MSI) is a form of genomic instability caused by impairments in the mismatch repair (MMR) system [5]. MSI is characterized by loss of expression of MMR genes, typically consequent to either genetic mutation or epigenetic inactivation of the MutL Homolog 1 (MLH1) and MutS Homolog 2 (MSH2) gene promoters [6][7][8]. MSI occurs in around 15% of all sporadic colorectal cancers [9] and is associated with right-sided tumors, lower tumor stage at diagnosis, better prognosis, improved survival, and reduced recurrence of metastasis [10][11]. In the early stages of colorectal cancer, it has been demonstrated that MSI status plays a role in predicting response to adjuvant therapy. In particular, it has been observed that patients with high microsatellite instability (MSI-H) do not benefit from 5-fluorouracil (5-FU) adjuvant therapy [10][12][13], whereas a significant survival benefit has been reported from the administration of B after chemotherapy (CT) [14]. Similarly, in the QUASAR 2 randomized study, the addition of B to capecitabine led to improved survival with respect to capecitabine alone in MSI-H patients and in those with microsatellite stability (MSS) [15]. These data suggest that MSI-H status may be associated with a better response to anti-angiogenic drugs in an adjuvant setting. A study performed in the metastatic setting showed no difference in progression-free survival (PFS) after chemotherapy with bevacizumab therapy in relation to MSI status [16]. Conversely, a recent study performed on a large case series from the Cancer and Leukemia Group B (CALGB)/SWOG 80405 trial reported that patients with MSI-H benefited more from bevacizumab than from cetuximab, highlighting the need to further investigate the role of MSI in relation to the efficacy of B [17].

    2. Development

    Elevated microsatellite alterations at selected tetranucleotide (EMAST) repeats are considered as a specific, non-standard, subtype of MSI and are caused by the defective translocation of MutS Homolog 3 (MSH3) to the cytosol rather than by genetic or epigenetic alterations in MMR genes. EMASTs are more frequent in colorectal cancers than MSI [18], and their presence is associate with advanced tumor stage, metastasis, poor survival, and intraepithelial inflammation [19][20][21][22]. The predictive role of EMAST has only partially been investigated [23][24], probably because the repeat types and thresholds used in EMAST analysis have still not been standardized. In the present study, we analyzed EMAST status in relation to prognosis in a series of mCRC patients treated with CT alone or CT + B, and we showed that the presence of EMAST instability was associated with a worse prognosis in the overall case series, with a trend that seemed more significant in the group of patients treated with CT + B. 

    As far as we know, there are no previous publications reporting similar data on the association between each specific EMAST marker and prognosis and response to mCRC treatments; only a few reports have measured the frequency of individual markers in mCRC patients. Two studies reported that, among EMAST markers, D20S8 was the locus with the highest frequency of frameshift alterations in mCRC [19][20], and that its instability was a direct consequence of hMSH3 deficiency in tumor cells [25]. This marker is located in the chromosome region of 20p12.3, which is typically associated with cancer susceptibility [26][27][28]. Alterations in the EMAST marker MYCL Proto-Oncogene, BHLH Transcription Factor (MYCL1) are strongly related to metastatic recurrence and poor survival of mCRC [29][30]. MYCL1 is a structurally complex microsatellite consisting of mono-, tetra-, and pentanucleotide repeats [31][32], but it is preferentially mutated in the tetranucleotide locus [33]. Kambara and colleagues hypothesized that this MYCL1 mutation, which is frequent in mCRC cancer, may indirectly promote tumor growth [34]. In our case series, MYCL1 was significantly associated with worse prognosis in patients treated with CT, being strongly indicative of poor OS.

    This entry is adapted from 10.3390/ijms21103532


    1. Ferlay, J.; Soerjomataram, I.; Dikshit, R.; Eser, S.; Mathers, C.; Rebelo, M.; Parkin, D.M.; Forman, D.; Bray, F. Cancer incidence and mortality worldwide: Sources, methods and major patterns in GLOBOCAN 2012. Int. J. Cancer 2015, 136, E359–E386.
    2. Siegel, R.L.; Miller, K.D.; Fedewa, S.A.; Ahnen, D.J.; Meester, R.G.S.; Barzi, A.; Jemal, A. Colorectal cancer statistics, 2017. CA Cancer J. Clin. 2017, 67, 177–193.
    3. Nappi, A.; Berretta, M.; Romano, C.; Tafuto, S.; Cassata, A.; Casaretti, R.; Silvestro, L.; De Divitiis, C.; Alessandrini, L.; Fiorica, F.; et al. Metastatic colorectal cancer: Role of target therapies and future perspectives. Curr. Cancer Drug Targets 2018, 18, 421–429.
    4. Cidon, E.U.; Alonso, P.; Masters, B. Markers of response to antiangiogenic therapies in colorectal cancer: Where are we now and what should be next? Clin. Med. Insights Oncol. 2016, 10, 41–55.
    5. Aaltonen, L.A.; Peltomaki, P.; Leach, F.S.; Sistonen, P.; Pylkkanen, L.; Mecklin, J.P.; Jarvinen, H.; Powell, S.M.; Jen, J.; Hamilton, S.R. Clues to the pathogenesis of familial colorectal cancer. Science 1993, 260, 812–816.
    6. Miyakura, Y.; Sugano, K.; Akasu, T.; Yoshida, T.; Maekawa, M.; Saitoh, S.; Sasaki, H.; Nomizu, T.; Konishi, F.; Fujita, S.; et al. Extensive but hemiallelic methylation of the hMLH1 promoter region in early-onset sporadic colon cancers with microsatellite instability. Clin. Gastroenterol. Hepatol. 2004, 2, 147–156.
    7. Herman, J.G.; Baylin, S.B. Gene silencing in cancer in association with promoter hypermethylation. N. Engl. J. Med. 2003, 349, 2042–2054.
    8. Koopman, M.; Kortman, G.A.M.; Mekenkamp, L.; Ligtenberg, M.J.L.; Hoogerbrugge, N.; Antonini, N.F.; Punt, C.J.A.; van Krieken, J.H.J.M. Deficient mismatch repair system in patients with sporadic advanced colorectal cancer. Br. J. Cancer 2009, 100, 266–273.
    9. Vilar, E.; Gruber, S.B. Microsatellite instability in colorectal cancer-the stable evidence. Nat. Rev. Clin. Oncol. 2010, 7, 153–162.
    10. Sinicrope, F.A.; Rego, R.L.; Foster, N.; Sargent, D.J.; Windschitl, H.E.; Burgart, L.J.; Witzig, T.E.; Thibodeau, S.N. Microsatellite instability accounts for tumor site-related differences in clinicopathologic variables and prognosis in human colon cancers. Am. J. Gastroenterol. 2006, 101, 2818–2825.
    11. Gryfe, R.; Kim, H.; Hsieh, E.T.; Aronson, M.D.; Holowaty, E.J.; Bull, S.B.; Redston, M.; Gallinger, S. Tumor microsatellite instability and clinical outcome in young patients with colorectal cancer. N. Engl. J. Med. 2000, 342, 69–77.
    12. Popat, S.; Hubner, R.; Houlston, R.S. Systematic review of microsatellite instability and colorectal cancer prognosis. J. Clin. Oncol. 2005, 23, 609–618.
    13. Jover, R.; Castells, A.; Llor, X.; Andreu, M. Predictive value of microsatellite instability for benefit from adjuvant fluorouracil chemotherapy in colorectal cancer. Gut 2006, 55, 1819–1820.
    14. Pogue-Geile, K.; Yothers, G.; Taniyama, Y.; Tanaka, N.; Gavin, P.; Colangelo, L.; Blackmon, N.; Lipchik, C.; Kim, S.R.; Sharif, S.; et al. Defective mismatch repair and benefit from bevacizumab for colon cancer: Findings from NSABP C-08. J. Natl. Cancer Inst. 2013, 105, 989–992.
    15. Kerr, R.S.; Love, S.; Segelov, E.; Johnstone, E.; Falcon, B.; Hewett, P.; Weaver, A.; Church, D.; Scudder, C.; Pearson, S.; et al. Adjuvant capecitabine plus bevacizumab versus capecitabine alone in patients with colorectal cancer (QUASAR 2): An open-label, randomised phase 3 trial. Lancet. Oncol. 2016, 17, 1543–1557.
    16. Kim, S.T.; Kim, H.K.; Lee, J.; Park, S.H.; Lim, H.Y.; Park, Y.S.; Kang, W.K.; Park, J.O. The impact of microsatellite instability status and sidedness of the primary tumor on the effect of bevacizumab-containing chemotherapy in patients with metastatic colorectal cancer. J. Cancer 2018, 9, 1791–1796.
    17. Innocenti, F.; Ou, F.-S.; Qu, X.; Zemla, T.J.; Niedzwiecki, D.; Tam, R.; Mahajan, S.; Goldberg, R.M.; Bertagnolli, M.M.; Blanke, C.D.; et al. Mutational analysis of patients with colorectal cancer in CALGB/SWOG 80405 identifies new roles of microsatellite instability and tumor mutational burden for patient outcome. J. Clin. Oncol. 2019, 37, 1217–1227.
    18. Carethers, J.M. Microsatellite instability pathway and EMAST in colorectal cancer. Curr. Colorectal Cancer Rep. 2017, 13, 73–80.
    19. Devaraj, B.; Lee, A.; Cabrera, B.L.; Miyai, K.; Luo, L.; Ramamoorthy, S.; Keku, T.; Sandler, R.S.; McGuire, K.L.; Carethers, J.M. Relationship of EMAST and microsatellite instability among patients with rectal cancer. J. Gastrointest. Surg. 2010, 14, 1521–1528.
    20. Lee, S.-Y.; Chung, H.; Devaraj, B.; Iwaizumi, M.; Han, H.S.; Hwang, D.-Y.; Seong, M.K.; Jung, B.H.; Carethers, J.M. Microsatellite alterations at selected tetranucleotide repeats are associated with morphologies of colorectal neoplasias. Gastroenterology 2010, 139, 1519–1525.
    21. Garcia, M.; Choi, C.; Kim, H.-R.; Daoud, Y.; Toiyama, Y.; Takahashi, M.; Goel, A.; Boland, C.R.; Koi, M. Association between recurrent metastasis from stage II and III primary colorectal tumors and moderate microsatellite instability. Gastroenterology 2012, 143, 48–50.e1.
    22. Carethers, J.M.; Koi, M.; Tseng-Rogenski, S.S. EMAST is a form of microsatellite instability that is initiated by inflammation and modulates colorectal cancer progression. Genes 2015, 6, 185–205.
    23. Watson, M.M.; Lea, D.; Rewcastle, E.; Hagland, H.R.; Soreide, K. Elevated microsatellite alterations at selected tetranucleotides in early-stage colorectal cancers with and without high-frequency microsatellite instability: Same, same but different? Cancer Med. 2016, 5, 1580–1587.
    24. Hamaya, Y.; Guarinos, C.; Tseng-Rogenski, S.S.; Iwaizumi, M.; Das, R.; Jover, R.; Castells, A.; Llor, X.; Andreu, M.; Carethers, J.M. Efficacy of adjuvant 5-fluorouracil therapy for patients with EMAST-positive stage II/III colorectal cancer. PLoS ONE 2015, 10, e0127591.
    25. Yang, X.; Zhang, Y.; Hosaka, K.; Andersson, P.; Wang, J.; Tholander, F.; Cao, Z.; Morikawa, H.; Tegner, J.; Yang, Y.; et al. VEGF-B promotes cancer metastasis through a VEGF-A-independent mechanism and serves as a marker of poor prognosis for cancer patients. Proc. Natl. Acad. Sci. USA 2015, 112, E2900–E2909.
    26. Bhattacharya, R.; Fan, F.; Wang, R.; Ye, X.; Xia, L.; Boulbes, D.; Ellis, L.M. Intracrine VEGF signalling mediates colorectal cancer cell migration and invasion. Br. J. Cancer 2017, 117, 848–855.
    27. Apte, R.S.; Chen, D.S.; Ferrara, N. VEGF in signaling and disease: Beyond discovery and development. Cell 2019, 176, 1248–1264.
    28. Giannakis, M.; Mu, X.J.; Shukla, S.A.; Qian, Z.R.; Cohen, O.; Nishihara, R.; Bahl, S.; Cao, Y.; Amin-Mansour, A.; Yamauchi, M.; et al. Genomic correlates of immune-cell infiltrates in colorectal carcinoma. Cell Rep. 2016, 15, 857–865.
    29. Jass, J.R.; Do, K.A.; Simms, L.A.; Iino, H.; Wynter, C.; Pillay, S.P.; Searle, J.; Radford-Smith, G.; Young, J.; Leggett, B. Morphology of sporadic colorectal cancer with DNA replication errors. Gut 1998, 42, 673–679.
    30. Liang, J.-T.; Huang, K.-C.; Lai, H.-S.; Lee, P.-H.; Cheng, Y.-M.; Hsu, H.-C.; Cheng, A.-L.; Hsu, C.-H.; Yeh, K.-H.; Wang, S.-M.; et al. High-frequency microsatellite instability predicts better chemosensitivity to high-dose 5-fluorouracil plus leucovorin chemotherapy for stage IV sporadic colorectal cancer after palliative bowel resection. Int. J. Cancer 2002, 101, 519–525.
    31. Fallik, D.; Borrini, F.; Boige, V.; Viguier, J.; Jacob, S.; Miquel, C.; Sabourin, J.-C.; Ducreux, M.; Praz, F. Microsatellite instability is a predictive factor of the tumor response to irinotecan in patients with advanced colorectal cancer. Cancer Res. 2003, 63, 5738–5744.
    32. Des Guetz, G.; Lecaille, C.; Mariani, P.; Bennamoun, M.; Uzzan, B.; Nicolas, P.; Boisseau, A.; Sastre, X.; Cucherousset, J.; Lagorce, C.; et al. Prognostic impact of microsatellite instability in colorectal cancer patients treated with adjuvant FOLFOX. Anticancer Res. 2010, 30, 4297–4301.
    33. Serrano, P.E.; Gu, C.-S.; Husien, M.; Jalink, D.; Ritter, A.; Martel, G.; Tsang, M.E.; Law, C.H.; Hallet, J.; McAlister, V.; et al. Risk factors for survival following recurrence after first liver resection for colorectal cancer liver metastases. J. Surg. Oncol. 2019, 120, 1420–1426.
    34. Tseng-Rogenski, S.S.; Chung, H.; Wilk, M.B.; Zhang, S.; Iwaizumi, M.; Carethers, J.M. Oxidative stress induces nuclear-to-cytosol shift of hMSH3, a potential mechanism for EMAST in colorectal cancer cells. PLoS ONE 2012, 7, e50616.