Association of p16 Homozygous Deletions with Clinicopathologic Characteristics and EGFR/KRAS/p53 Mutations in Lung Adenocarcinoma

Abstract

Purpose:Thep16 geneis frequentlyinactivatedinlungadenocarcinoma.Inparticular,homozygous deletions (HD)havebeenfrequentlydetectedincelllines; however, their frequencyandspecificityis not well-established in primary tumors.The purpose of this study was to elucidate the prevalence and the timing for the occurrence of p16 HDs inlung adenocarcinoma progression in vivo. Experimental Design: Multiple ligation-dependent probe amplification was used for the detection of p16 HDs in 28 primary small-sized lung adenocarcinomas and 22 metastatic lung adenocarcinomas to the brain. Cancer cells were isolated from primary adenocarcinoma specimens by laser capture microdissection. HDs were confirmed by quantitative real-time genomic PCR analysis. Results: HDs were detected in 8 of 28 (29%) primary tumors, including 2 of 8 (25%) noninvasive bronchioloalveolar carcinomas, and 5 of 22 (26%) brain metastases, respectively. No significant associations were observed between p16 HDs and gender, age, smoking history, stage, and prognosis. HDs were detected with similar frequencies (17^29%) among adenocarcinomas with epidermal growth factor receptor (EGFR) mutations, with KRAS mutations, and without EGFR/KRAS mutations, and with similar frequencies (22^28%) between adenocarcinomas with and without p53 mutations. Conclusions: p16 HDs occur early in the development of lung adenocarcinomas and with similar frequencies among EGFR type, KRAS type, and non-EGFR/KRAS type lung adenocarcinomas. Tobacco carcinogens would not be a major factor inducing p16 HDs in lung adenocarcinoma progression.

Whole Genome Comparison of Allelic Imbalance between Noninvasive and Invasive Small-Sized Lung Adenocarcinomas

“…Therefore, 13q13 alterations were suggested to contribute to the formation of noninvasive tumors irrespective of EGFR/KRAS mutation. We recently reported that p16 homozygous deletions also occur with similar frequencies (f25%) in noninvasive and invasive tumors, in replacement and nonreplacement growth types, and among three groups according to the status of EGFR/KRAS mutations (8). The p16 gene is located on chromosome 9p, which was a hotspot/critical region of AI in both noninvasive and invasive tumors.…”

“…The status of EGFR/ KRAS/TP53 mutations in 30 cases was previously reported (6,8). Fortytwo cases were newly analyzed in this study for mutations in exons 18 to 21 of the EGFR gene, in exons 1 to 2 of the KRAS gene, and in exons 4 to 8 of the TP53 gene by genomic PCR and direct sequencing as described previously (6).…”

“…The EGFR and KRAS genes are mutually exclusively mutated in lung adenocarcinomas, and inhibition of activities of these mutants led to the inhibition of adenocarcinoma cell growth (2)(3)(4)(5). EGFR and KRAS mutations have been detected both in noninvasive and invasive adenocarcinomas (6)(7)(8); therefore, these alterations are considered to be critical for the development of lung adenocarcinomas, irrespective of their invasiveness. Recently, we showed that p16 homozygous deletions occur at similar frequencies (f25%) in noninvasive and invasive adenocarcinomas, whereas the frequency of p53 mutations in invasive ones was much higher than that in noninvasive ones (8).…”

“…EGFR and KRAS mutations have been detected both in noninvasive and invasive adenocarcinomas (6)(7)(8); therefore, these alterations are considered to be critical for the development of lung adenocarcinomas, irrespective of their invasiveness. Recently, we showed that p16 homozygous deletions occur at similar frequencies (f25%) in noninvasive and invasive adenocarcinomas, whereas the frequency of p53 mutations in invasive ones was much higher than that in noninvasive ones (8). However, phenotypic diversities of adenocarcinomas cannot be explained only by accumulation of these genetic alterations.…”

“…18) and a small volume, only a limited number of small-sized adenocarcinomas have been examined for a few genetic alterations, including EGFR, KRAS, and TP53 mutations and allelic imbalance (AI) of a few chromosomal loci (6)(7)(8)19). However, a subset of the alterations, including TP53 mutations, have been detected more frequently in invasive tumors than in noninvasive tumors.…”