Quantitative analysis of effect of neodymium-YAG laser on transplanted mouse carcinomas

Intradermally transplanted non-immunogenic murine carcinomas measuring 3-6 mm in diameter were exposed to a neodymium-YAG laser beam (1060 nm) over a range of exposure times (0.5-6 seconds) and energy densities (expressed as watts/mm2 exposure field). Subsequent growth of the irradiated tumours was compared with that of untreated tumours. A clear dose-response relationship dependent only on power delivered per unit area was found. Below a given dose threshold (about 2 joules/mm2) the tumours continued to grow at the same rate as the control tumours although an effect of irradiation could be seen histologically. Above this threshold the tumours completely disappeared but by 10-14 days started to regrow at a rate slightly greater than in the control mice; the reason for this increased rate remains to be determined. At the highest doses (above about 5.5 joules/mm2) there was complete regression and skin healing, with no evidence of local recurrence in seven animals and with no evidence of distant metastases in six out of seven up to 12 months later, a result not previously achieved by surgical excision. The laser provides a controlled and simply applied method of tumour eradication. This animal model gives a quantitative basis for further studies of the effects of laser irradiation on tumour growth.