INTRODUCTION
By far, the most common human malignancy is skin cancer. The incidence is increasing at an astonishing rate, with more than 5.4 million new cases of non-melanoma skin cancer (NMSC) diagnosed each year in the United States1 that is 925 new skin cancers diagnosed each hour awake! The most common causative factor is excessive exposure to sunlight, which cannot be avoided with our daily occupational and recreational activities. The rapid rise is enhanced not only by increased travel with vacations in sunny environments, but also by an increase in high risk groups, such as immunocompromised organ transplant patients.2-4 The most directly carcinogenic spectrum of sunlight is ultraviolet B (UVB) radiation,5 both a tumor initiator and promoter.6-8 Generation of reactive oxygen species (ROS) by UVB exposure not only induces oxidative DNA damage, leading to not only tumor initiation,9 but also to activation of many growth factors and signal transduction cascades including those involved in tumor promotion, such as tyrosine protein kinase (TPK) and mitogen activating protein (MAP) kinase pathways.10-12 UVB-induced inflammation and immunosuppression further contribute to photocarcinogenesis.11 Therefore, topical or systemic supplementation by antioxidants may protect skin against UVB-induced photodamage and carcinogenesis.13 With current emphasis on preventative medicine and healthy eating, recent research for new anticancer drugs focuses more on natural nutrients from the regular human diet. These compounds rarely cause adverse side effects, and they act on a wide range of molecular targets involved in carcinogenesis. Lycopene is a carotenoid found in tomatoes and other red-colored fruits and vegetables.14 This powerful dietary antioxidant has received considerable attention in recent years. A potent scavenger of oxygen radicals, lycopene has the highest singlet oxygen quenching ability when compared to 31 other antioxidants.15-17 Numerous epidemiological, in vitro and animal studies provide convincing evidence that lycopene prevents a variety of cancers,18 including prostate,19-21 breast,22-24 cervical,25 gastric,26 colon,27 lung,28,29 liver,30,31 bladder,32 and renal cell cancers.33 Only recently have studies assessed whether lycopene has potential for prevention of skin cancer.34,35 Although the anticarcinogenic effects of lycopene are thought to be primarily due to its antioxidant properties,36 other mechanisms have also been demonstrated, such as enhancing the gap junctional communication (GJC),37 suppressing the growth factor receptor signaling,38,39 inducing the apoptosis of cancerous cells,34,40 regulating the cell cycle.38,41 and stimulating the immune system.42
