Necessity of Microdissecting Different Tumor Components in Pulmonary Tumor Pyrosequencing

Microdissection is a useful method in tissue sampling prior to molecular testing. Tumor heterogeneity imposes new challenges for tissue sampling. Different microdissecting methods have been employed in face of such challenge. We improved our microdissection method by separately microdissecting the morphologically different tumor components. This improvement helped the pyrosequencing data analysis of two specimens. One specimen consisted of both adenocarcinoma and neuroendocrine components. When both tumor components were sequenced together for KRAS (Kirsten rat sarcoma viral oncogene homolog) gene mutations, the resulting pyrogram indicated that it was not a wild type, suggesting that it contained KRAS mutation. However, the pyrogram did not match any KRAS mutations and a conclusion could not be reached. After microdissecting and testing the adenocarcinoma and neuroendocrine components separately, it was found that the adenocarcinoma was positive for KRAS G12C mutation and the neuroendocrine component was positive for KRAS G12D mutation. The second specimen consisted of two morphologically different tumor nodules. When microdissected and sequenced separately, one nodule was positive for BRAF (v-raf murine sarcoma viral oncogene homolog B1) V600E and the other nodule was wild type at the BRAF codon 600. These examples demonstrate that it is necessary to microdissect morphologically different tumor components for pyrosequencing.