Analysis of K-ras oncogene mutation directly applied to atypical cell clusters on cytologic smear slides of bile and pancreatic juice

To develop an objective reference for the cytological evaluation of atypical cells in bile and pancreatic juice, we analyzed K-ras oncogene mutation In atypical cell clusters, which were collected directly from cytological smear slides; 50 samples (cell clusters) from 31 smear slides of 21 patients with carcinomas of the pancreatic head region, and nine samples from eight cases of benign disease. These cell clusters (5–1000 cells/cluster) were selectively suspended In buffer containing proteinase K, and subjected to DNA extraction. K-ras codon 12 mutation was determined by polymerase chain reaction amplification, followed by digestion with BstNI. The K-ras gene was amplified in 20 of 21 cases with carcinoma (34/50 samples), and In seven of eight cases with non-neoplastic disease (8/9 samples). Among the cases of which primary tumors showed K-ras mutation, amplification was successful in 10 of 11 cases; mutation was demonstrated in three of seven cases with cytologically atypical cells (4/11 samples), and in three of three cases with cytologically malignant cells (5/7 samples). No mutation was Identified in the 10 cases of carcinoma without K-ras mutation (0/15 samples), or in eight cases of non-neoplastlc disease (0/8 samples). Cytological details could be comparatively evaluated between atypical cell clusters with or without mutation on the same smear slides in two cases. This type of direct analysis of atypical cell clusters may be useful in the self-assessment of cytological diagnosis of bile and pancreatic juice.