TPC1 cells carry a paracentric inversion of chromosome 10 causing the recombination of the tyrosine kinase-encoding domain of the ret receptor to the 5′-terminal region of the H4 gene, leading to the generation of the ret/ptc1 oncogene (Ishizaka et al, 1990), a lesion commonly found in papillary carcinomas (Grieco et al, 1990). This evidence concerns the gene RET and thyroid gland papillary carcinoma.