Mitotic phase distribution, mitotic activity and apoptosis in basal cell tumours of canine skin

This study evaluates the mitotic phase distribution, mitotic activity and apoptosis in 17 basal cell tumours of canine skin. The number of mitotic and apoptotic cell/mm2 of neoplastic epithelium is counted and the volume corrected mitotic and apoptotic index, respectively, are obtained (M/V and A/V index). Transmission electron microscopy is performed on selected cases to confirm the typical features of apoptosis. The M/V index ranges from 9 to 45/mm2 of neoplastic epithelium, while the A/V index ranges from 5 to 111/mm2 of neoplastic epithelium. Even if the number of apoptotic cells is slightly higher than that of mitotic cells and vice versa, the mean values of the two parameters (mean M/ V = 20.76 +/- 10.86, mean A/V = 31.41 +/- 24.53) tend to be equal. In fact, apoptotic and mitotic index are not statistically different (P = 0.11). Furthermore, in all the samples examined, an increased proportion of metaphases (46.82%) is observed. These findings suggest that the discrepancy between apparent mitotic activity and tumour growth may be mainly due to the increased duration of the entire cell cycle rather than to the high incidence of apoptosis.