KRAS Amplification Is Restricted to KRAS Mutated Lung Adenocarcinomas.
Simion Chiosea, Carol Sherer, Sanja Dacic. University of Pittsburgh Medical Center, PA
Background: KRAS mutations are well studied in lung carcinoma, but their relationship with KRAS amplification was rarely reported. Recent studies suggested that combination of KRAS mutation with amplification may indicate worse prognosis. The aim of our study was to determine the frequency of KRAS amplification in lung adenocarcinomas (ADC) in respect to oncogenic mutations, and their clinicopathologic characteristics. The allelic imbalance between KRAS mutated allele (MA) and wild type allele (WTA) was also assessed.
Design: 122 surgically resected, formalin fixed, paraffin embedded lung ADC (73 KRAS mutated, 20 EGFR mutated, 29 wild type) were randomly selected for KRAS FISH analysis. Dual color FISH was performed using a Spectrum Green- labeled chromosome 12 centromeric probe (Abbott Molecular, Des Plaines, IL) and a Spectrum-Orange labeled, locus specific KRAS (RP11-295I5, CHORI, Oakland, CA) probe. KRAS /CEP12 ratio ≥ 2 was considered positive for amplification. To characterize the incidence and significance of allelic imbalance between KRAS mutated allele (MA) and wild type allele (WTA), sequencing electropherograms (SE) were semi-quantitatively scored and categorized in two groups: MA>WTA or MA≤WTA.
Results: KRAS amplification was identified in 5 out of 122 ADC (4%), all of which harbored KRAS mutation (5/73; 7%). The 3 cases with KRAS mutation and amplification presented at higher stage and experienced worse survival. Four cases showed predominant solid morphology. KRAS mutated cases with MA>WTA demonstrated KRAS amplification, validating SE as a quantitative method of evaluating the “dosage” of KRAS MA. None of KRAS mutated cases negative for KRAS amplification showed MA>WTA.
Conclusions: KRAS amplification seems to occur in KRAS mutated ADC only and may have poor prognostic implications. A semi-quantitative evaluation of KRAS allelic imbalance may help to identify cases with KRAS amplification and should be considered to be a part of routine reports of KRAS sequencing. Further studies of prognostic and therapeutic impact of the KRAS MA level and KRAS amplification are warranted.
Monday, February 28, 2011 1:30 PM
Platform Session: Section E, Monday Afternoon