Warts and
squamous cell carcinomas are important cutaneous complications in organ transplant recipients. The role of
infection with human papillomaviruses (HPV) in the development of cutaneous
squamous cell carcinoma is still unclear. An extremely diverse group of HPV types, mainly consisting of
epidermodysplasia-verruciformis (EV)-associated HPV types, can be detected in benign, premalignant, and malignant skin lesions of organ transplant recipients. Frequently, there are multiple HPV types present in single skin biopsies. Typically, the prevalence of viral
warts rises steadily after
transplantation and a strong association exists between the number of HPV-induced
warts and the development of
skin cancer. The interval between the
transplantation to the development of
warts is clearly shorter than the interval from
transplantation to the diagnosis of the first
skin cancer. A comparison of transplant recipients with and without
skin cancer, however, showed an equally high prevalence of EV-HPV
DNA in keratotic skin lesions in both groups of patients and the detection rate and spectrum of
HPV infection in hyperkeratotic
papillomas,
actinic keratoses, and
squamous cell carcinomas was also similar. HPV
DNA can frequently be detected in patients with hyperproliferative disorders like
psoriasis and
antibodies against HPV in patients with regenerating skin (e.g., after extensive second degree
burns).
Latent infection with EV-HPV seems to be widespread. The hair follicle region might be the reservoir of EV-HPV. The E6
protein from a range of cutaneous HPV types effectively inhibits apoptosis in response to UV-light induced damage. It is therefore conceivable that individuals who are infected by EV-HPV are at an increased risk of developing
actinic keratoses and
squamous cell carcinomas, possibly by chronically preventing UV-light induced apoptosis.