CA4 and cancer: Combretastatins CA-4 4a, (phosphate prodrug 4b), CA-1 4c (phosphate prodrug 4d), 4e, and serine prodrug ombrabulin 4f (Figure 1b) have demonstrated impressive antiproliferative potency with microtubule destabilising and anti-vascular effects in many cancers, including breast cancer [48,49,50].