Somatic mutations in the exonic sequences of STK11/LKB1. A: PX68 (lanes 2) and PX68-1A (lanes 3) are two parallel xenografts of the same pancreatic cancer, and both exhibited the same somatic nucleotide substitution that created a stop codon (a non-sense mutation). The mutation was not detected in the normal tissue of the patient (PN68, lanes 1 and 4). Lanes 5 belong to another pancreatic tumor xenograft, which did not harbor a somatic mutation in STK11/LKB1. The arrow points to the site of the mutation. B: Xenograft tumor PX104 (lanes 1) and its corresponding primary cancer, PC104 (lanes 3), harbored the same nucleotide deletion, which was not detected in the normal tissue of the patient (PN104, lanes 2) or in another pancreatic xenograft (lanes 4). The arrow indicates the site of the mutation.