PIK3CA mutation status in Japanese lung cancer patients

doi:10.1016/j.lungcan.2006.07.006

Lung Cancer

Volume 54, Issue 2, November 2006, Pages 209-215

https://doi.org/10.1016/j.lungcan.2006.07.006 Get rights and content

Summary

Somatic mutations of the PIK3CA (phosphatidylinostitol 3-kinase catalytic subunit) gene have been found in human cancer patients. Previous reports suggested that about 4% of lung cancers harbored PIK3CA gene mutations. However, the clinico-pathological background for PIK3CA gene mutations has not yet been investigated in lung cancer. We have genotyped the PIK3CA gene in Japanese lung cancer patients. The study included 235 lung cancer cases surgically removed in Nagoya City University Hospital. The two PIK3CA mutation hot spots (exon 9 and exon 20) were analyzed by real time polymerase chain reaction (PCR)-based assay. The data were confirmed by direct sequencing. In exon 9, somatic mutation was found in eight patients (3.4%). The mutation included three E542K (G1624A), three E545K (G1633A), one E542Q (G1624C), and one Q546K (C1636A). However, in exon 20, there was no mutation in our lung cancer patients. PIK3CA mutations were not correlated with gender (women versus men, p = 0.4162), age (≤60 versus >60, p = 0.8027), or smoking status of the lung cancers (never versus smoker, p = 0.5666). PIK3CA mutation incidence was significantly lower in adenocarcinoma (2/135, 1.5%) than in squamous cell carcinoma (5/77, 6.5%, p = 0.0495). Among eight patients with a PIK3CA mutation, three patients also harbored an EGFR somatic mutation. PIK3CA gene mutations were rare in lung cancer; rarer in adenocarcinoma. Further functional analyses of the PIK3CA mutations are warranted to study if they could be the target of therapy for the lung cancer.

Introduction

It is now well established that cancer is a genetic disease and that somatic mutation of the oncogene and tumor suppressor genes are the initiator of the carcinogenic process [1]. The phosphatidylinositol 3-kinase signaling pathway has recently been suggested to play a pivotal role in the oncogenesis of human cancers [1].

Recently, high frequencies of somatic mutation in the PIK3CA gene have been reported in several cancer types, including colon, brain, stomach, breast, and ovary [2], [3], [4], [5], [6], [7]. More than 75% of these mutations are clustered in the helical (exon 9) and kinase domains (exon 20) of the PIK3CA gene [2]. Mutations in the three mutation hotspots in PIK3CA (i.e., E542K, E545K, and H1047R) have been shown to elevate its lipid kinase activity and lead to the activation of the downstream Akt-signaling pathway [2], [8]. The PIK3CA mutation was identified in 4% of lung cancer cases, however, this particular study included only one case with the mutation [2].

For known mutations, real time polymerase chain reaction followed by melting curve analysis, using hybridization probes, is highly sensitive, rapid, and an efficient approach to mutation detection [9], [10], [11]. To determine the PIK3CA mutation status in Japanese lung carcinoma for screening and diagnostic purpose, we wanted to develop a faster and easy method to detect mutations. In this report, we investigated PIK3CA mutation status by the real time PCR-based assay using LightCycler [12] wild type specific sensor an anchor probes. The PIK3CA gene was then sequenced to confirm the PCR study. The findings were analyzed in reference to the clinico-pathologic features of the lung cancer.

Section snippets

Patients

The study groups included 235 lung cancer patients who had undergone surgery at the Department of Surgery II, Nagoya City University Medical School between 1997 and 2003. The lung tumors were classified according to the general rule for clinical and pathological record of lung cancer in Japan [13]. All tumor samples were immediately frozen and stored at −80 °C until assayed.

The clinical and pathological characteristics of the 235 lung cancer patients are as follows; 116 cases at stage I, 47 at

Genotyping of PIK3CA at exon 9 and exon 20 in lung cancer tissues

For the PCR-based genotyping of the exon 9 of PIK3CA, the anchor probe was matched for the wild type sequence. As shown in Fig. 1a, wild type PCR product showed a single peak at 64 °C, whereas the heterozygous products (mutant) showed an additional peak at 57 °C. Among the 235 lung cancer patients, 12 patients had a single additional peak. As shown in Fig. 1b, the homozygous wild type PCR product showed a single peak at 69 °C in the PCR-based genotyping for the exon 20. However, no additional peak

Discussion

We obtained findings that 3.4% (8/235) of the lung cancer samples harbored a mutation in the exon 9 of the PIK3CA gene. This was in good agreement with a previous report that PIK3CA gene mutation was found in 4% of lung cancers [2]. Interestingly, the PIK3CA mutation incidence was lower in adenocarcinoma than in squamous cell carcinoma (Table 1), in sharp contrast with the predominance of adenocarcinoma in tumors with an EGFR mutation [14], [15], [16], [17], [19], [20]. This may indicate that

Acknowledgments

The authors would like to thank Mrs. Yuri Yamamoto for her excellent technical assistance.

Grant Support: Supported by the Grant-in-Aid for Science Research (Nos. 17390385, 18659407, 18390381, and 18790998) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), and AstraZeneca Research Grant 2004.

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PIK3CA mutation status in Japanese lung cancer patients

Summary

Introduction

Section snippets

Patients

Genotyping of PIK3CA at exon 9 and exon 20 in lung cancer tissues

Discussion

Acknowledgments

Hum Mutant

Mol Diagn

Lung Cancer

Biochem Biophys Res Commun

J Biochem Biophys Methods

Cancer Genet Cytogenet

Lung Cancer

Eur J Cancer

Mutation of the PIK3CA oncogene in human cancers

Br J Cancer

High frequency of mutations of the PIK3CA gene in human cancers

Science

The PIK3CA gene is mutated with high frequency in human breast cancers

Cancer Biol Ther

PIK3CA gene is frequently mutated in breast carcinomas and hepatocellular carcinomas

Oncogene

Mutation of the PIK3CA gene in ovarian and breast cancer

Cancer Res

Mutations of PIK3CA gene in anaplastic oligodendrogliomas, high-grade astrocytomas, and medulloblastomas

Cancer Res

Phosphatidylinositol 3-kinase mutations identified in human cancer are oncogenic

Proc Natl Acad Sci USA

Continuous fluorescence monitoring of rapid cycle DNA amplification

Biotechniques