Macroscopical and histopathological changes in regressing primary and recurrent equine sarcoids during active specific bio-immunotherapy. 
Healing sarcoids were followed in 18 horses which had taken part in previous clinical studies on a total of 29 horses suffering from either primary or recurrent sarcoids, treated with bio-immunotherapy.  In the present study, attention was paid to changes observed in these fibroblastic skin tumours during their regression.  The tumours were surgically debulked leaving the base in the skin.  The horses were immunized according to bio-immunotherapy at 2- to 4-week intervals with an autogenous vaccine made from the excised part of the tumour until the base had visibly regressed.  Healing was followed by inspections and serial biopsies from the base, studied under light microscope.  Visibly normal epithelisation developed first at the margin of the base, progressing gradually to the centre.  The mean rate of epithelisation was approximately equal to normal horse skin.  Most of the histopathological features typical of equine sarcoid diminished significantly in the follow-up biopsies, when the first signs of visibly normal epithelisation were observed.  The changes were more evident among the primary than the recurrent tumours.  No leucocyte infiltration, lysis or apoptosis were found during the regression.  Bio-immunotherapy seems to simulate a spontaneous healing process.