CACNA1E and cancer: Clinical observations that altered expression of β-tubulin isotypes in cancer are associated with altered sensitivity to TBAs are supported by in vitro studies noting altered expression of βII-, βIVa-, βIVb and βV-tubulin isotype expression in a range of drug-resistant cancer cell lines [29,40,49,50,51,52,53,54,55,56,57,58,59].