The in vitro effects of a single exposure of LASER irradiation on human breast carcinoma and immortalised human mammary epithelial cell lines. Katie Powell(1&2), Dr Liisa Laakso(2), Dr Ann McDonnell(1), Dr Pauline Low(2), Dr Steve Ralph(2); Griffith University, Brisbane(1) and Gold Coast(2), Australia. PURPOSE: This research examined the cell proliferative response of two breast cancer cell lines and two immortalised human mammary epithelial cell lines in vitro to a range of doses of low level laser therapy (LLLT) at wavelengths of 780 nm, 830 nm and 904 nm. RELEVANCE: LLLT is used in the clinical treatment of post-mastectomy lymphoedema, although specific information on safety is scant and circumstantial. This presentation describes the first steps in gaining disease-specific knowledge upon which to develop guidelines for the safe clinical use of lasers in the management of post-mastectomy lymphoedema. METHODS: Human breast adenocarcinoma (MCF-7), human breast ductal carcinoma (MDA-MB-435S) and immortalised human mammary epithelial (SVCT and Bre80hTERT) cell lines were irradiated with a single exposure of laser at 0.5, 1, 2, 3, 4, 10 and 12 J/cm2 (?=780 nm) and 0.5, 1, 2, 3, 4, 10 and 15 J/cm2 (?=830 nm and 904 nm). Cell proliferation was assessed 24 hours after laser using XTT colorimetric assays. RESULTS: SVCT cell proliferation significantly increased after exposure to doses of 0.5, 1, 2, 3, 4, and 12 J/cm2 of laser at 780 nm and doses of 0.5, 1, 2, 4 and 10 J/cm2 of laser at 904 nm. The MDA-MB-435S and Bre80hTERT cell lines showed negligible effects with one exposure from all three wavelengths of laser and no dose response relationships were noted. The MCF-7 cells demonstrated an increasing dose response relationship with one exposure of 780 nm laser; and there were no dose response effects evident after exposure to 830 nm and 904 nm laser irradiation. CONCLUSIONS: Even though certain doses of laser increased MCF-7 cell proliferation, the amount of laser light penetrating through the skin clinically is considerably attenuated. Further in vivo research of LLLT is required before a definitive conclusion can be made regarding the safety of LLLT for post-mastectomy lymphoedema.