Long-term immunosuppression causes a significantly increased risk for the development of malignancies in transplanted patients. A link between immunosuppression and incidence of cancer is well documented and involves the effect of immunosuppression on anti-tumor surveillance and antiviral adaptive immune responses. We present a 67-year-old patient with a history of recurrent non-melanoma skin cancer. After adjustment of immunosuppressive therapy under close pharmacodynamic control, the development of new malignant lesions could be prevented. The availability of a quantitative, quick laboratory test for an assessment of the individual functional activity of immunocompetent cells that are crucial for transplant rejection, defense against viral infection, and tumor surveillance along with the ability to adjust doses of immunosuppressive agents such that patients are largely protected against malignant disease and/or viral infection are important. NFAT-regulated gene expression measured in peripheral blood allowed us to predict "safe" immunosuppression. Thus patients could maintain a stable allograft function. This represents a breakthrough in transplantation medicine and advances our attempts to individualize treatment in transplanted patients.