Cancer cells given vinblastine would be unable to separate chromosomes during cell division.
It is shown that the effect of vinblastin depends on its concentration, at very low concentrations it suppresses microtubule dynamics and at higher concentrations it reduces microtubule polymer mass.
Microtubules are part of the cell's apparatus for dividing and replicating itself, so inhibition of these structures results in halting the cell division and thus, cell death.