Epidermolysis bullosa (EB) is a heritable skin disease characterized by marked fragility of epithelialized tissue with blistering in skin and mucous membranes following the slightest mechanical trauma. Eighty percent of all patients suffering from recessive dystrophic EB (RDEB), a subtype originating from mutations in the COL7A1 gene, develop squamous cell carcinoma (SCC). In RDEB patients SCC presents early (most patients are in their 20s or 30s) and shows a highly aggressive metastatic course which often leads to premature death at this young age. In light of scarce data on the efficacy and safety of systemic treatment regimens for advanced SCC, the investigators propose to perform a small, first in EB trial of an experimental drug called rigosertib for the treatment of EB cancer. The trial will be conducted in two study centres, in London and Salzburg, and will last approximately 2.5 years with each patient recruited being in the study for 1 year. The drug is a polo-like kinase inhibitor interfering with different molecular pathways that are essential for cancer cell growth. Rigosertib was developed by Onconova Therapeutics and is currently tested in several clinical trials for a number of other cancers including myelodysplastic syndrome (a cancer of the blood). The investigators have identified that rigosertib most selectively kills EB cancer cells in vitro while leaving normal EB skin cells unaffected. This project will evaluate whether rigosertib is capable of inducing an anti-cancer response in EB patients and whether the drug is well-tolerated. Mechanisms of molecular targeting of squamous cancer cells by rigosertib will further be investigated in EB patients, also aiming at the identification of biomarkers that may allow the predictive identification of best responders.