Representative image of tumour with macroscopic areas of necrosis. Tumour analysis from patient 6. (a) Macroscopic view of ex vivo liver tissue with extensive tumour infiltration, including viable (blue box) and necrotic (white box) areas. (b) H&E section (magnification ×2) of tissue from areas of strong 131I-huA33 uptake in macroscopically viable tumour [blue box in (a) and (d)] showing numerous viable tumour clusters with occasional necrotic/acellular areas. (c) H&E section (magnification ×2) of tissue from area of reduced uptake of 131I-huA33 [white box in (a) and (d)] showing areas of extensive stroma and necrosis but with some islands of viable tumour. (d) Corresponding ex vivo gamma camera image of tumour from (a) showing 131I-huA33 uptake in all macroscopic tumour but highest uptake in viable areas (blue box), lesser uptake in necrotic areas (white box), and no specific uptake in normal liver tissue (upper right edge of specimen). (e, f) Corresponding autoradiographs from (b) and (c), respectively, showing high uptake in all viable tumour islands, demonstrating that the apparent lack of uptake in macroscopically necrotic tissue is a function of reduced cell number rather than reduced antibody penetration or cellular uptake.