The Phototumorigenic Potential of Broad-Band (270–350 nm) and Narrow-Band (311–313 nm) Phototherapy Sources Cannot Be Predicted by Their Edematogenic Potential in Hairless Mouse Skin

Abstract

The new Philips TL01 narrow-band (311-313 nm) and conventional broad-band (e.g., Philips TL12; 270-350 nm) sources are effective for psoriasis phototherapy, for which treatment regimens are based on a predetermined minimal erythema dose. TL01 phototherapy treatment times are approximately half those with TL12 for psoriasis, whereas the cumulative exposure doses at clearing are similar. We compared the phototumorigenic potential of TL01 and TL12 radiation in mouse skin. Groups of albino Skh-1 hairless mice were exposed for 5 d/week at three dose levels. At each dose level, TL12 and TL01 doses were equally edematogenic. At each dose level, TL01 radiation was significantly more effective at producing first tumors of 1 mm in diameter and multiple tumors. At the lower two dose levels, TL01 radiation produced a significantly greater proportion of squamous cell carcinomas. This study demonstrates that TL01 radiation is more phototumorigenic than TL12 radiation at equally edematogenically weighted doses. This is in contrast with previous reports that edema production by polychromatic sources is predictive of their phototumorigenic effect in Skh-1 mice. The absolute cumulative TL12 dose needed to induce tumors was much less than that for TL01 radiation. The possibility of increased tumor risk with TL01 phototherapy should be considered but must be balanced against the high phototherapeutic efficacy of this source, short treatment times, and the low cumulative doses necessary for clearing of psoriasis.

Phototherapy and Photochemotherapy for Psoriasis

“…27,28 This has not been shown in European studies. Although in mice NB-UV-B was more carcinogenic than BB-UV-B at equally erythemogenic doses, 29 follow-up of patients receiving extensive UV-B treatments did not demonstrate an increase in skin cancer incidence. 30,31 However, most of the available studies had an observation time shorter than 5.6 years, which might be too short to detect skin cancer as a long-term risk of phototherapy.…”

Narrowband UV-B Phototherapy vs Photochemotherapy in the Treatment of Chronic Plaque-Type Psoriasis

“…The assessment of cancer risk resulting from the clinical use of narrowband UV-B is based on retrospective studies on broadband UV-B-treated patients 6,7,27,28 and on mouse studies comparing the carcinogenicity of broadband vs narrowband UV-B. 13,[29][30][31] These data suggest that the cancer risk of equitherapeutic doses of narrowband UV-B is not greater than that of broadband UV-B and substantially lower than that of PUVA. 32,33 This assumption has recently gained further support from an in vitro study indicating that phototherapy with narrowband UV-B does not produce more DNA damage than treatment with broadband UV-B.…”

Formation of 8‐hydroxy‐2′‐deoxyguanosine in the DNA of cultured human keratinocytes by clinically used doses of narrowband and broadband ultraviolet B and psoralen plus ultraviolet A

“…Narrowband UVB phototherapy has thus significantly improved the therapeutic efficacy of conventional broadband UVB (290 -320 nm) phototherapy for skin diseases such as psoriasis, atopic dermatitis, vitiligo and others. (10)(11)(12)(13) Narrowband UVB is widely used in the treatment of skin disease, and the current trend toward the increased use of narrowband UVB phototherapy is justified.(14) Its carcinogenic potential is judged to be substantially less than that of psoralen plus UVA (PUVA) photochemotherapy.(15) Although the results of studies in mice indicate that narrowband UVB could induce more skin cancers than broadband UVB therapy, (16) the participants in a workshop on the use of narrowband UVB in phototherapy concluded that the long-term human cancer risk should be no greater than that with broadband phototherapy. (17) When the DNA damage in keratinocytes induced by narrowband or broadband UVB was measured by single cell gel electrophoresis (comet assay), narrowband UVB produced less DNA damage than broadband UVB at equal doses.…”

“…(15) Although the results of studies in mice indicate that narrowband UVB could induce more skin cancers than broadband UVB therapy, (16) the participants in a workshop on the use of narrowband UVB in phototherapy concluded that the long-term human cancer risk should be no greater than that with broadband phototherapy. (17) When the DNA damage in keratinocytes induced by narrowband or broadband UVB was measured by single cell gel electrophoresis (comet assay), narrowband UVB produced less DNA damage than broadband UVB at equal doses.…”