The risk of squamous cell and basal cell cancer associated with psoralen and ultraviolet A therapy: a 30-year prospective study.

BACKGROUND: By 1977, psoralen and ultraviolet A (PUVA) was established as a highly effective therapy for psoriasis. Because of concerns about potential long-term adverse effects, particularly cancer, the PUVA Follow-Up Study was established to assess long-term risk and benefits of PUVA. OBJECTIVE: We sought to determine the association of certain squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) risk with exposure to PUVA. METHODS: For nearly 30 years, this prospective cohort study of 1380 patients with psoriasis first treated with PUVA in 1975 to 1976 documented exposures and incident events including biopsy-proven skin cancers. RESULTS: From 1975 to 2005, 351 of 1380 (25%) cohort patients developed 2973 biopsy-proven SCC and 330 (24%) developed 1729 BCCs. After adjusting for age, gender, and significant confounders, the risk of developing one or more SCC in a year was strongly associated with total number of PUVA treatments (350-450 vs <50 treatments, incidence rate ratio [IRR] = 6.01, 95% confidence interval [CI] = 4.41-8.20). When all tumors are included this risk is significantly higher (IRR = 20.92, 95% CI = 14.08-31.08). Corresponding risks for BCC were much lower (person counts IRR = 3.09, 95% CI = 2.36-4.06; tumor counts IRR = 2.12, 95% CI = 1.47-3.05). LIMITATIONS: This was an observational prospective study of a cohort with severe psoriasis. An unknown factor associated with higher dose exposure to PUVA in our cohort that was not included in our analysis could account for the observed associations. CONCLUSION: Exposure to more than 350 PUVA treatments greatly increases the risk of SCC. Exposure to fewer than 150 PUVA treatments has, at most, modest effects on SCC risk. Even high-dose exposure to PUVA does not greatly increase BCC risk. The risks of SCC in long-term PUVA-treated patients should be considered in determining the risk of this therapy relative to other treatments for severe psoriasis.

1,2-Dimethylhydrazine-induced colon carcinoma and lymphoma in msh2(-/-) mice.

BACKGROUND: Defective mismatch repair (MMR) in humans is particularly associated with familial colorectal cancer, but defective repair in mice is generally associated with lymphoma in the absence of experimental exposure to carcinogens. Loss of MMR also confers resistance to the toxic effects of methylating agents. We investigated whether resistance to methylation contributes to increased susceptibility to colorectal cancer in mice by exposing mice with defects in the MMR gene msh2 to a methylating agent. METHODS: Tumor incidence and time of death in msh2(+/+), msh2(+/-), and msh2(-/-) mice were analyzed after weekly exposure (until tumor appearance) to the methylating agent 1,2-dimethylhydrazine (DMH). Chemically induced and spontaneous tumors were characterized by frequency, type, and location. The tumor incidence in untreated and treated mice of each genotype was compared by a Mann-Whitney U test. Carcinogen-induced apoptosis in histologic sections of small and large intestines was also determined. All statistical tests were two-sided. RESULTS: Homozygous inactivation of the msh2 gene statistically significantly accelerated (P<.0001) death due to the development of DMH-induced colorectal tumors and lymphomas. Rates of death from DMH-induced colorectal adenocarcinoma were similar in msh2 heterozygous and wild-type mice, but only msh2 heterozygotes (msh(+/-)) developed additional, noncolorectal malignancies (notably trichofolliculoma [two of 21], angiosarcoma of the kidney capsule [two of 21], and lymphoma [one of 21]), suggesting that heterozygosity for msh2 slightly increases DMH susceptibility. DMH induced apoptosis in small intestinal and colonic epithelial crypts that was dependent on active msh2. CONCLUSIONS: Inactivation of msh2 allows the proliferation of gastrointestinal tract cells damaged by methylating agents. Furthermore, MMR constitutes a powerful defense against colorectal cancer induced by DNA methylation.

Expression of enhancing factor/phospholipase A2 in skin results in abnormal epidermis and increased sensitivity to chemical carcinogenesis.

Enhancing factor (EF), a growth factor modulator, is the mouse homologue of human secretory group II phospholipase A(2). EF exhibits growth-promoting activity in vitro, in the presence of epidermal growth factor, and also brings about phenotypic transformation of normal cells. In order to ascertain the role of EF in vivo, a human keratin-14 promoter was used to drive the expression of EF ectopically to squamous epithelial cells. The founder mouse and its progeny showed abnormal whiskers and a scaly, beaded tail. In these mice, keratinization pattern of the epidermis was disturbed and parakeratosis and acanthosis were noted. The transgenic mice, TgK14-EF, expressed EF in the suprabasal layers of tail epidermis as well as in the epithelial cells of hair follicle and sebaceous glands of skin. Expression of EF along with hyperplasia was also observed in other squamous epithelia such as buccal mucosa, tongue and oesophagus. TgK14-EF mice homozygous for the transgene showed delayed and scanty hair growth although the mice were healthy and fertile. The hemizygous TgK14-EF mice were sensitive to a two-stage chemical carcinogenesis and developed a higher number of papillomas than their normal littermates over the course of the experiment. The conversion rate of papilloma to carcinoma was two fold higher in the transgenic mice.