ORIGINAL ARTICLE T [20] repeat in the 3′-untranslated region of the MT1X gene: a marker with high sensitivity and specificity to detect microsatellite instability in colorectal cancer Luca Morandi & Dario de Biase & Michela Visani & Adriana Monzoni & Annalisa Tosi & Mauro Brulatti & Daniela Turchetti & Paola Baccarini & Giovanni Tallini & Annalisa Pession Accepted: 10 November 2011 /Published online: 23 November 2011 # Springer-Verlag 2011 Abstract Purpose Stratifying patients defective in mismatch repair (dMMR) with high microsatellite instability (MSI-H) in colorectal cancer (CRC) is of increasing relevance and may provide a more tailored approach to CRC adjuvant therapy. Here, we describe the discovery of a new MSI marker for colorectal cancer located in the 3′-untranslated region (3′ UTR, T20 mononucleotide repeat) of the metallothionein 1X gene (MT1XT20). Methods We studied 340 consecutive CRCs using three multiplexed polymerase chain reactions amplifying BAT25, BAT26, TGFBR2, MybT22, BAT40, MT1XT20, NR21, NR24, CAT25, D2S123, D5S346, D17S250, D18S58, CSF1PO, D7S820, and D18S51. Fragments length was evaluated by automated capillary electrophoresis. Results Based on the NCI/ICG-HNPCC criteria for MSI classification, 40 CRCs were found to be MSI-high (11.8%), 46 (13.5%) CRCs were MSI-low, and 254 CRCs (74.7%) were stable (MSS). MT1XT20 showed very high sensitivity (97.3%) comparable to BAT26 (97.5%) and CAT25 (97.1%) and the best specificity (100%) as well as MybT22 and CAT25. Indeed, MT1XT20 instability was detected in 36 out of 37 cases (97.3%) of MSI-high colorectal cancers, whereas no MT1XT20 alterations were observed in 254 MSS or in 46 MSI-low cases. On the contrary, BAT40 was found to be unstable in 8/46 MSI-low cases, BAT25 in 6/46, BAT26 4/46, NR21 1/46, and NR24 in 1/45. Conclusions Our results suggest that MT1XT20 represents a sensitive and specific marker for MSI testing and could be included in a complete set of MSI markers for the confident identification of familial or sporadic dMMR patients in CRCs. Electronic supplementary material The online version of this article (doi:10.1007/s00384-011-1365-7) contains supplementary material, which is available to authorized users. L. Morandi : D. de Biase : M. Visani : A. Tosi : P. Baccarini : G. Tallini Department of Haematology and Oncological Sciences L. and A. Seragnoli, Section of Anatomic Pathology at Bellaria Hospital, University of Bologna, via Altura 3, 40139 Bologna, Italy D. de Biase : M. Visani : A. Pession Department of Experimental Pathology, University of Bologna, via San Giacomo 14, 40126 Bologna, Italy A. Monzoni Alphagenics Diaco Biotechnologies S.r.l., Area Science Park SS14, Basovizza, Trieste, Italy M. Brulatti General Surgery, Bellaria Hospital A.U.S.L. Bologna, via Altura 3, 40139 Bologna, Italy D. Turchetti Medical Genetics Unit, Polyclinic S. Orsola-Malpighi, University of Bologna, Bologna, Italy L. Morandi (*) Sezione di Anatomia Patologica “M. Malpighi”, Dipartimento di Ematologia e Scienze Oncologiche “L. e A. Seragnoli”, Università di Bologna, Ospedale Bellaria, via Altura 3, 40139 Bologna, Italy e-mail: l.morandi@ausl.bo.it Int J Colorectal Dis (2012) 27:647–656 DOI 10.1007/s00384-011-1365-7