Regression of canine cutaneous histiocytoma: reduced proliferation or increased apoptosis?

Background/aim: Canine cutaneous histiocytoma (CCH) is a tumour that undergoes spontaneous regression. The aim of this study was to establish a possible relationship between regression of CCH and tumoural cell proliferation and apoptosis.

Materials And Methods: Immunostaining with Ki-67 antigen and the terminal deoxytransferase (TdT) deoxyuridine-5'-triphosphated (dUTP) nick-end labelling (TUNEL) method were performed on 93 specimens of CCH, grouped into four histological groups.

Results: The proliferative index evaluated with Ki-67 antigen expression was on average 23.56 ± 7.91%. The apoptotic index determined by the TUNEL method was on average 39.37 ± 5.87%. Neither the proliferative nor apoptotic index differed between histological groups. Moreover, the proliferative and apoptotic indices did not correlate significantly. However, apoptotic activity was higher than proliferative activity in almost all tumours.

Conclusion: A reduction of proliferation or an increase of apoptosis does not appear to justify regression of CCH. However, our results suggest that an imbalance between cell proliferation and apoptotic cell death plays a significant role in spontaneous regression of CCH.