Epithelial malignancies in organ transplant patients: clinical presentation and new methods of treatment.

Transplantation of solid organs has been well established as a mode of therapy for the treatment of various end-stage organ diseases for many years. Up to now, it has benefited more than 1 million patients worldwide. The long-term success of organ transplantation depends particularly on the prevention of allograft rejection. Various regimens have been used to suppress hosts' cellular immune responsiveness to the grafted organs. Nowadays immunosuppressive therapies consist mainly in prednisolone, azathioprine, cyclosporine, anti-T-lymphocyte-globulin (ATG), anti-CD 3 antibody (OKT3) and substances of a new generation, such as tacrolimus or mycophenolic acid. However, not only the patient's reactivity to the graft is impaired, but also that to infectious organisms. Chronically altered immune responsiveness is especially associated with a dramatically increased risk of malignancy, most frequently non-Hodgkin's lymphoma and skin cancer. Within the first 5 years of immunosuppression 40% of transplant recipients experience premalignant skin tumors such as actinic keratoses and Bowen's disease, and also such skin cancers as squamous cell carcinomas and basal cell carcinomas. Quite often these have an aggressive biology and an uncommon morphology. Cancer is now responsible for a mortality rate of 5-8% in organ transplant patients. Various risk factors, such as exposure to sun and infections with oncogenic viruses (e.g. HPV) contribute to the already increased risk of dysplasia when lifelong immunosuppression is required. Prophylactic strategies therefore include the development of virus-like particles (VLPs) as anticancer vaccines, which might become a very interesting approach to preventing HPV-associated cancer. The prevention of precancerous conditions and mature skin cancers in grafted patients includes protective clothing and adequate protection of UV-exposed skin regions, including lips, from sunlight with appropriate sunscreen. Close dermatological surveillance through a specialized outpatient department should be ensured to detect potentially fatal skin malignancies at an early stage. Early treatment of precancerous lesions includes topical retinoids, such as tretionin, tazarotene or adapalene. A 5% fluorouracil cream is widely used but shows variable effects on manifest actinic keratoses. As cellular immunity seems to play the major part in the prevention and cure of malignant and premalignant cutaneous neoplasias as well as viral infections, a specific enhancement of the local immunity would be desirable. Imiquimod is one of a class of agents known as immune response modifiers. The drug has been shown to have both antiviral and antitumor activity. Application of immune response activators or modifiers such as imiquimod might be premising in the case of transplant recipients.