<p>Nude mice xenografted with A-431 tumor cells were i.p. injected with (A) NaCl, the irrelevant <sup>212</sup>Pb-PX, (B) unlabeled (40 µg) or <sup>212</sup>Pb-labeled 35A7 (anti-CEA), or (C) unlabeled (40 µg) or <sup>212</sup>Pb-labeled tratsuzumab (anti-HER2). Mice were sacrificed when the bioluminescence signal reached 2.0×10<sup>9</sup> photons/s and median survival estimated using the Kaplan–Meier method. Censored mice are indicated by vertical bars.</p