SERPINB2 and cancer: McDevitt et al (2000) reported that 213Bi-J591 can regress the growth of LNCaP spheroids comprising ∼1000 cancer cells in vitro. This in vitro result also supports our in vivo targeting results. All of these findings indicate that 213Bi-PAI2 may target cancer cells in the very early micrometastatic stage, i.e. cells in transit or at the pre-angiogenic stage, while larger solid tumours exhibited a growth reduction, but not complete regression. Therefore, small multiple metastatic sites or minimum residual disease should be considered to be the most suitable targets for 213Bi-PAI2.