Ultrastructural changes in regressing equine sarcoid tumours--mysterious role of mitochondria.

Mitochondrial changes of healing sarcoids were followed in 17 affected horses. Biopsies of this fibroblastic skin tumour were collected both before and during the treatment and tumour regression. The therapy consisted of the partial excision of tumours, repeated immunizations with autogenous polymerized tumour particles and supportive dietary treatment with stannic chloride and folic acid. Presence of transformed, electron-dense mitochondria in different phases of healing was studied by successive biopsy from regressing tumours. Additionally, the relation of these transformed mitochondria to the clinical status and behaviour of the tumours was evaluated. Transformed mitochondria were not found in the tumour tissue of the horses that had not been earlier treated by bioimmunotherapy, while after the therapy, all of the regressing tumours showed electron dense mitochondria. These changes were found significantly more in the margin of the regressing tumours than at the centre, i.e. at the site where the visible healing had further progressed. There was no difference between the numbers of transformed mitochondria in the horses with initially a primary or recurrent tumour. However, horses that developed recurrent disease after bioimmunotherapy showed significantly smaller numbers of electron-dense mitochondria as a response to bioimmunotherapy than the horses which did not experience relapse. Mitochondrial changes seem to be dynamically linked to the healing process and, additionally, may reflect prognosis.