The morphological effects of vincristine sulfate on canine bone marrow cells

This study documents the morphologic changes observed in the bone marrow aspirate biopsies from dogs 6 and 24 hours after receiving a single therapeutic dose (0.025 mg/kg) of vincristine sulfate (Oncovin: Eli Lilly & Co., Indianapolis, Ind.) intravenously. The most striking cytologic changes were observed in the erythroid cell line. Abnormalities included increased numbers of mitotic figures, abnormal nuclear configurations, and fragmented nuclei. Erythroid cells in metaphase were prominent in marrow samples collected 6 hours post-vincristine, accounting for a mean of 27% of all erythroid precursors. Fragmented nuclei and atypical nuclear configurations were seen in low numbers (mean = 7%) of erythroid cells from these animals. In contrast, marrow collected from dogs 24 hours post-vincristine exhibited low numbers (mean = 1%) of erythroid cells in metaphase, but erythroid cells with atypical nuclear configurations and fragmented nuctei accounted for a mean of 41% of the erythroid cells present. Less dramatic increases in the number of mitotic non-erythroid cells were seen 6 hours post-vincristine (mean = 5% of non-erythroid cells) and 24 hours post-vincristine (mean = 1% of non-erythroid cells). Only rare nuclear fragmentation was observed in these cell lines. Significant alterations in megakaryocytes and myeloid to erythroid (M:E) ratios were not observed in samples taken 6 hours post-vincristine; however, M:E ratios were considerably higher in three of the four samples taken from dogs 24 hours post-vincristine. Similar time-related changes were observed in four clinical cases in which bone marrow aspirates were performed after vincristine administration.