## 4 Discussion  
In this study we evaluated gene expression, survival, and body composition of ccRCC patients with VHL and TTN gene mutations. The decreased expression of VHL and the increased expression of TTN in KIRC based on sample types was shown (Figures 1 and 2). Furthermore, while the expression levels of VHL on KIRC patient survival did not show a significant difference, a TTN high expression level showed a link with shorter survival (Figures 3 and 4). Indeed, ccRCC patients with VHL low/medium expression show a survival probability greater than 0.25 and a maximum survival greater than eight years, while ccRCC patients with TTN high expression show a survival probability lower than 0.25 and lower maximum survival (around eight years). Moreover, our results showed a significant decrease of TAT, VAT, SAT and TAM in the ccRCC-TTN group compared to the ccRCC-VHL group (Figures 5 and 6). The role of adipose tissue, especially VAT, in the pathogenesis of RCC is known. In fact, both ccRCC patients and non-ccRCC patients showed an increased amount of VAT [10; 11; 26]. Furthermore, the relationship between VAT and VHL and KDM5C gene mutations has been recently reported [27]. Increased adipose tissue determines the abnormal secretion of adipokines and the release of hypoxia-inducible factor 1 (HIF-1) following the insufficient supply of oxygen [28; 29; 30]. The complex of proteins related to VHL protein leads to HIF degradation, and with the inactivation of the VHL gene the lack of HIF degradation could develop angiogenesis and cell growth [31; 32; 33; 34]. Long non-coding RNAs are a group of non-protein coding RNA transcripts [31]. They were considered \"transcriptional junk\", but recently it has been shown that they can play an important regulatory role in various diseases including cancer [35; 36]. Many long non-coding RNAs have been shown to play a regulatory role in ccRCC progression by acting both as tumor suppressors and oncogenes [37]. It has recently been shown that long non-coding antisense RNA TTN 1 (TTN-AS1) is overexpressed in many malignancies including lung adenocarcinoma, gastric cancer and colorectal cancer [38; 39; 40; 41]. A recent study investigated the expression, molecular mechanisms and function of TTN-AS1 in ccRCC in order to improve understanding of the ccRCC progression [37]. They demonstrated that TTN-AS1 knockdown suppressed cell proliferation of ccRCC, suggesting a possible role as oncogene [37]. This data can help in the development of new therapeutic strategies. The reduction of abdominal adipose tissue compartments and abdominal muscle mass in the ccRCC-TTN group compared to the ccRCC-VHL group might be linked to TTN  
Figure 6: Axial CT images showing VAT segmented in orange, TAM segmented in pink salmon and SAT segmented in yellow in ccRCC-VHL patient (**A**) and ccRCC-TTN patient (**B**), clearly showing the decreased amount of VAT, TAM and SAT in the ccRCC-TTN patient. Please note that this is a demonstrative figure to show the main massage of this study and not a figure explaining the methods of body composition segmentation (please see methods section for a detailed description). gene mutation. In fact, the ccRCCC-VHL group showed a better survival trend compared with the ccRCCC-TTN group. Furthermore, these body composition differences in ccRCCC patients with TTN gene mutation could be used as a biomarker of tumor mutational burden. Currently, molecular mechanisms and the pathogenic activity of TTN gene mutation in ccRCC are not fully understood. Further studies will have to include larger samples of ccRCC patients with TTN gene mutation in order to confirm the relationship between the observed decreased survival in ccRCC patients with TTN gene mutation and changes of body composition towards cancer cachexia. Here, for the first time, we suggested a correlation between CT derived body composition and VHL and TTN expression in ccRCCC, and our data are likely to stimulate further studies on the topic.