Updated project metadata. Keratinocyte carcinomas (KC) are the most common malignancy worldwide. This category of tumours groups both basal (BCC) and squamous (SCC) cell carcinomas. While the former rarely metastasizes (0.03-0.55%), the latter is more associated to a substantial risk of local recurrence, metastasis and death (1.5-4%). In addition, it is well known that the extracellular signals from tumour cells are involved in most of the steps triggering metastasis. This pro-metastatic signalling is mediated by proteins secreted by cancer cells, which constitute the tumour secretome and can be obtained from tumour interstitial fluid (TIF). The TIF baths the tumour and stromal cells and characterizes the tumour microenvironment. The proteomic study of TIF is of particular interest for explaining the metastatic potential of a tumour. In this work, we have analysed the proteomic composition of the TIF from BCC and SCC tumour biopsies and discovered a new set of extracellular proteins that could be useful as differential biomarkers. In addition, these proteins may help to understand the distinct invasive and metastatic abilities of the KC.