In previous studies, the expression of the protein SPARC was shown to predict longer OS [7, 11, 12]. Nevertheless, the IHC expression on formalin-fixed paraffin embedded tissues of other ECM components, such as FN1 or their combination, has not been investigated so far. In the present study, we show that DLBCL cases with expression of FN1 present with longer OS. Moreover, in our cohort the combined expression of FN1 and SPARC is a better predictor for longer OS than the markers taken separately. Since our study comprises mostly cases diagnosed before the introduction of Rituximab as treatment option, only 49 patients received this drug in our cohort. When the analysis for OS was performed in this subgroup of patients no significant difference based on SPARC, FN1 or the combination of both markers was found, possibly due to the low number of cases (data not shown).
Our results, generated by IHC, recapitulate data from a GEP study on a large number of DLBCL. The authors identified several genes of the ECM, and grouped them into so-called stromal signatures, able to predict survival . Stromal-2 signature genes included markers for endothelial cells and key regulator for angiogenesis. In contrast, stromal-1 signature encoded components of the ECM, such as various collagen and laminin isoforms, as well as FN1 and SPARC. In accordance with its role in ECM formation, staining for FN1 localized to the fibrous strands in our lymphomas. SPARC staining, instead, highlighted endothelial cells and non-neoplastic cells, which were identified as macrophages in previous studies, based on CD68 expression [7, 11]. Even though several data suggest that the composition of ECM is of major importance in the tumourigenesis, the exact functions of SPARC and FN1 in DLBCL have not been studied so far. To this regard, the role of SPARC could be related to its regulatory activity in several signalling pathways, such as TGFβ and PI3K/AKT. Moreover, SPARC has been shown to bind to FN1 fragments and to induce matrix metalloproteinases (MMP) which degrade ECM components .
Our results, together with data derived from studies on tumour microenvironment performed in other tumour types, might open new diagnostic and therapeutic possibilities. To this regard, both FN1 and SPARC are being tested as biomarkers in different clinical trials (see http://clinicaltrials.gov, identifiers: NCT01288963, NCT01442974, NCT01566435). In addition, new therapeutic strategies targeting the ECM components are being evaluated, such as specific molecules inhibiting the interaction between FN1 and tumour cells or therapeutic agents conjugated to antibodies specific for tumour environment. For example, interleukin-2 has been conjugated to an antibody specific for the FN1 isoform containing the extradomain-B, EDB, which is expressed during tissue remodelling in tumours [13, 14].
In conclusion, our results show that the combined IHC expression of FN1 and SPARC can be used in the routine clinical practice as predictor of survival in patients suffering from DLBCL, recapitulating the data derived from GEP studies. This suggests that both the ECM component FN1 and the ECM remodelling SPARC can influence the survival of lymphoma cells and their interactions with the microenvironment.