High doses of laser phototherapy can increase proliferation in melanoma stromal connective tissue
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It is well established that laser phototherapy (LP) is contraindicated directly over cancer cells, due to its bio modulatory effects in cell and blood vessel proliferation. The aim of the present study was to analyze the influence of typical low-level laser therapy (LLLT) and high intensity laser therapy (HILT) and an in-between dose of 9 J on collagen fibers and blood vessels content in melanoma tumors (B16F10) implanted in mice. Melanoma tumor cells were injected in male Balb C mice which were distributed in four groups: control (no irradiated) or irradiated by 3, 9, or 21 J (150; 450, or 1050 J/cm2). LP was performed in daily sessions for 3 days with a InGaAlP—660 nm (mean output: 50 mW, spot size: 2 mm2). Tumor volume was analyzed using (1) picrosirius staining to quantify collagen fibers content and (2) Verhoeff’s method to quantify blood vessels content. Tumor growth outcome measured in the 3-J group was not significantly different from controls. Nine and 21-J groups, presented significant and dose-dependent increases in tumor volume. Quantitative analysis of the intensity of collagen fibers and their organization in stroma and peri-tumoral microenvironment showed significant differences between irradiated and control group. Blood vessels count of 21-J group outnumbered the other groups. High doses (≥ 9 J) of LP showed a dose-dependent tumor growth, different collagen fibers characteristics, and eventually blood vessel growth, while a typical LLLT dose (3 J) appeared harmless on melanoma cell activity.
KeywordsPhotobiomodulation LLLT Melanoma Collagen Bloob vessels Growing tumor
Compliance with ethical standards
All experiments were carried out in accordance with the guidelines from Cruzeiro do Sul University Bioethical Council for human and animal care, PROTOCOL 011/07.
Conflict of interest
The authors declare that they have no conflict of interest.
Professor Ernesto Cesar Pinto Leal-Junior received research support from Multi Radiance Medical (Solon, OH), a laser device manufacturer.
All authors agree to the submission of this manuscript.
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