Clonality and field cancerization in intraductal papillary-mucinous tumors of the pancreas.

Background: Multiple lesions of intraductal papillary-mucinous tumor of the pancreas (IPMT) in the same pancreas often are encountered. To elucidate field (multicentric) cancerization and clonality of IPMT, clonal analyses of IPMT and its precursor lesion of ductal hyperplasia were performed. K-ras codon 12 mutations and X-chromosome inactivation of human androgen receptor gene (HUMARA) were investigated.

Methods: Paraffin embedded tissue samples from the pancreata of 37 patients who underwent resection for IPMTs were microdissected manually or by laser capture microdissection. Multiple samples from each surgical specimen were microdissected representing each IPMT and discrete ductal hyperplasias. DNA was extracted, and K-ras codon 12 mutations were examined by two-step polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). The mutations were analyzed by direct DNA sequence. The HUMARA locus was digested with or without HpaII and HhaI prior to amplification. The HUMARA assay was conducted by fluorescence-labeled PCR-RFLP and was analyzed with specialized software.

Results: All 37 pancreata had at least two lesions of ductal hyperplasia, and 23 of 37 pancreata (62%) had K-ras codon 12 mutations in these precursor lesions. Of 23 pancreata with mutated K-ras hyperplasia, 15 (65%) had multiple, distinct mutations in different lesions of hyperplasia in the same pancreas, suggesting a field defect. Thirty-two of 37 IPMTs (86%) had K-ras codon 12 mutations. Among these, 16 IPMTs (50%) had multiple, distinct mutations at K-ras codon 12. The HUMARA assay showed that 12 of 15 IPMTs were informative, and 9 were considered polyclonal and/or oligoclonal origin in origin. With the combined results of multiple K-ras mutation detection and the HUMARA assay, 12 of 15 IPMTs from female patients (80%) were considered polyclonal and/or oligoclonal in origin.

Conclusions: The current results suggest that multiple, distinct K-ras mutations of different ductal hyperplasias in a given pancreas are due to a field (multicentric) cancerization effect in IPMTs. Thus, most of IPMTs are polyclonal and/or oligoclonal in origin, i.e., IPMTs may originate from multiple (molecularly distinct) precursor lesions.