Laser-activated cancer therapy: a low power red argon laser passes through four optical fibre waveguides to treat a cancer in a woman's throat. Unlike some other medical lasers, the beam does not destroy cancer cells by generating heat energy. Rather, it is used to activate a drug, haematoporphyrin derivative (HPD), previously injected into the patient. HPD does not affect normal cells, but is strongly absorbed by cancerous ones & the products of the photochemical reaction initiated by the laser are toxic to cancerous cells. Endoscopy allows this therapy to be extended to cancers of the lung & oesophagus.