RT Journal Article SR Electronic T1 Regression of Canine Cutaneous Histiocytoma: Reduced Proliferation or Increased Apoptosis? JF Anticancer Research JO Anticancer Res FD International Institute of Anticancer Research SP 1397 OP 1400 VO 33 IS 4 A1 PIRES, ISABEL A1 ALVES, ANABELA A1 QUEIROGA, FELISBINA LUISA A1 SILVA, FILIPE A1 LOPES, CARLOS YR 2013 UL http://ar.iiarjournals.org/content/33/4/1397.abstract AB 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.