Colorectal cancers with microsatellite instability are characterized by an important density of tumor-infiltrating lymphocytes and a good prognosis. Microsatellite instability results from the inactivation of the DNA mismatch repair system and induces secondary somatic frameshift mutations within target genes harboring repeat sequences in their coding frame. By disrupting the open reading frame, frameshift mutations can result in the appearance of potentially immunogenic neopeptides. To determine the frameshift mutations inducing a T-cell response during the development of a tumor with microsatellite instability, we studied in 61 colorectal cancer patients with microsatellite instability, using a fluorescent multiplex PCR comparative analysis, the relative frequency of frameshift mutations within 19 target genes and analyzed the correlation of these frameshift mutations with the density of CD3 þ tumor-infiltrating lymphocytes. The four most frequently mutated genes were ACVR2 (92%), TAF1B (84%), ASTE1/HT001 (80%) and TGFBR2 (77%). The vast majority (95%) of the tumors exhibited at least three frameshift mutations, and the number of frameshift mutations was associated with tumor progression (TNM stage, wall invasion and tumor diameter). Tumor-infiltrating lymphocyte density was associated with the overall number of frameshift mutations and with the presence of frameshift mutations within two target genes, namely ASTE1/HT001 and PTEN. These results strongly argue for the clinical relevance of immunotherapy of colorectal cancers with microsatellite instability.

Plexiform fibromyxomas are rare neoplasms, being officially recognized as a distinct entity among benign mesenchymal gastric tumors in the 2010 WHO Classification of Tumors of the Digestive System. Characteristically, these tumors have a multinodular/plexiform growth pattern, and histologically contain variably cellular areas of bland myofibroblastic type spindle cells embedded in an abundant myxoid matrix, rich in capillary-type vessels. As of yet, the molecular and/or genetic features of these tumors are unknown. Here, we describe a recurrent translocation t(11;12)(q11;q13) involving the MALAT1 (metastasis associated lung adenocarcinoma transcript 1) long noncoding gene and the GLI1 (glioma-associated oncogene homologue 1) gene in a subgroup of these tumors. The presence of the fusion transcript in our index case was confirmed using polymerase chain reaction on genomic DNA followed by Sanger sequencing. We showed that the truncated GLI1 protein is overexpressed and retains its capacity to transcriptionally activate its target genes. A specific FISH assay was developed to detect the novel MALAT1-GLI1 translocation in formalin-fixed paraffin-embedded material. This resulted in the identification of two additional cases with this fusion, and two cases with polysomy of the GLI1 gene. Finally, immunohistochemistry revealed that the GLI1 protein is exclusively overexpressed in those cases that harbor GLI1/12q13 genomic alterations. In conclusion, overexpression of GLI1 through a recurrent MALAT1-GLI1 translocation or GLI1 upregulation delineates a pathogenically distinct subgroup of plexiform fibromyxomas with activated Sonic Hedgehog signaling pathway.

Programmed death-1 (PD-1) is involved in T-cell tolerance to self-antigens. For some cancers, it has been suggested that the expression of a ligand of PD-1, namely PD-L1, could contribute to tumor escape from immune destruction. Nevertheless, the relationship between PD-1 expression on tumor-infiltrating T lymphocytes (TILs), disease stage, and TIL responsiveness is still poorly documented. In this study, we show that freshly isolated CD4(+) and CD8(+) TILs express substantial levels of PD-1 in primary melanomas. The expression of PD-1 was further increased at later stages in distant cutaneous metastases, especially on CD8(+) TILs. The expression of PD-1 ligands was frequent only in metastases, on both tumor cells and tumor-derived myeloid cells. TILs isolated from these cutaneous tumors are poorly reactive ex vivo, with blunted calcium response and IFN-γ production after TCR stimulation. Surprisingly, in distinct parts of a primary melanoma, either invasive or regressing, we show that TILs similarly express PD-1 and remain dysfunctional. The expressions of PD-1 and PD-L1 in metastatic melanoma lesions could be considered as witnesses of an unsuccessful anti-tumoral immune response, but the direct involvement of PD-1 in the severity of the disease, and the importance of TILs in tumor regression, remain to be established.