A photodynamic therapy experiment on 118 inbred white mice with transplanted Ehrlich's tumor (mouse
mammary gland adenocarcinoma) is performed to reveal mechanisms of necrosis formation. In 7-10 days the tumor of
1-1.5 cm diameter is formed under skin at the injection point, and PDT procedure is applied. There were used a chlorine
type photosensitizer RadachlorineTM and 662 nm wavelength diode laser. The drug is injected by intravenously at the
dose of 40 mg/kg; the irradiation is executed in 2-2.5 hours at the surface dose of about 200 J/cm2. Each of the mice had
a photochemical reaction in form of destructive changes at the irradiation region with subsequent development of dry
coagulation necrosis. After rejection of the necrosis there occurred epithelization of defect tissues in a tumor place.
Histological investigations were conducted in different follow-up periods, in 5 and 30 min, 1, 3, 6, and 12 hours, 1, 3, 7
and 28 days after irradiation. They included optical microscopy, immune marker analysis, morphometry with
measurements of volume density of epithelium, tumor stroma and necroses, vascular bed. The investigations showed that
an important role in damaging mechanisms of photodynamic action belongs to hypoxic injuries of tumor mediated by
micro vascular disorders and blood circulatory disturbances. The injuries are formed in a few stages: microcirculation
angiospasm causing vessel paresis, irreversible stases in capillaries, diapedetic hemorrhages, thromboses, and
thrombovasculitis. It is marked mucoid swelling and fibrinoid necrosis of vascular tissue. Progressive vasculitises result
in total vessel obliteration and tumor necrosis.