Novel mutant‐enriched sequencing identified high frequency of PIK3CA mutations in pharyngeal cancer

Abstract

We previously reported 4 PIK3CA mutations in 38 head and neck cancer samples, 3 of which were identified in 6 pharyngeal cancer samples. To determine the mutation frequency of PIK3CA in pharyngeal cancer, we studied 24 additional cases of pharyngeal squamous cell carcinoma in this study. Using both direct genomic DNA sequencing and novel mutant-enriched sequencing methods developed specifically for the 3 hot-spot mutations (H1047R, E545K and E452K) of PIK3CA, we detected 5 mutations of PIK3CA in the 24 pharyngeal cancers (20.8%). Three of the 5 mutations had been missed by the conventional sequencing method and were subsequently detected by novel mutant-enriched sequencing methods. We showed that the mutant-enriched sequencing method for the H1047R hot-spot mutation can identify the mutation in a mixed population of mutant and wild-type DNA sequences at 1:360 ratios. These novel mutant-enriched sequencing methods allow the detection of the PIK3CA hot-spot mutations in clinical specimens which often contain limited tumor tissues (i.e., biopsy specimens). The data further support that oncogenic PIK3CA may play a critical role in pharyngeal carcinogenesis, and the mutant-enriched sequencing methods for PIK3CA are sensitive and reliable ways to detect PIK3CA mutations in clinical samples. Because PIK3CA and its pathway are potential targets for chemotherapy and radiation therapy, and frequent somatic mutation of PIK3CA has been identified in many human cancer types (e.g., breast cancer, colorectal cancer), the abilities to detect PIK3CA mutations with enhanced sensitivities have great potential impacts on target therapies for many cancer types. ' 2007 Wiley-Liss, Inc.Key words: mutant-enriched sequencing method; PIK3CA oncogene; hot-spot mutation; pharyngeal cancer; HNSCC Oral and pharyngeal cancer accounts for over half a million new cancer cases and 2,710,000 deaths worldwide per annum. It is the sixth most common malignant tumors in the world. In the United States alone, there were 30,990 estimated new cancer cases and 7,430 new deaths in the oral cavity and pharynx in 2006. 1 Despite recent advances in surgical techniques and improvement in radiation therapy, the median survival of patients with head and neck cancer has changed little over the past few decades. 2 Thus, a better understanding of molecular and genetic feature of head and neck cancer would be critically helpful for the development of new methods for early diagnosis, monitoring and targeting therapy, and the eventual improvement in the survival rate. Recently, significant progress has been achieved in the understanding of the molecular genetic events underlying the development of oral squamous cell carcinoma, which includes inactivation of multiple tumor suppressor genes (p16, p53, p14 and FHIT) and activation of oncogenes (cyclin D1 and EGFR). 3,4 However, the molecular genetic profile of pharyngeal carcinogenesis is relatively less understood.PIK3CA, which is a member of PI3Ks family, has been demonstrated to function as an oncogene in some human ...

Clinicopathological significance of ROCK1 and PIK3CA expression in nasopharyngeal carcinoma

“…PIK3CA mutations are typically detected in a wide range of cancers, including head and neck squamous cell carcinoma, colorectal cancer and breast cancer (23)(24)(25)(26)(27). In the present study, high levels of PIK3CA expression were detected in 62.96% of the NPC specimens.…”

The molecular pathogenesis of head and neck squamous cell carcinoma

“…Loss of just a single PTEN allele in the remaining samples may contribute to tumorigenesis, however, since recent data suggesting a gene dosage effect for PTEN (69). Activating mutations in two "hot spot" regions of the PIK3CA gene occur in 6%-11% of HNSCCs, with a potential enrichment in tumors originating from the pharynx (70,71). The latter finding is particularly noteworthy given the increased incidence of PIK3CA mutations in HPV-related versus non-HPV-related tumors observed in both exome sequencing studies.…”

Frequent mutations and amplifications of the PIK3CA gene in pituitary tumors

“…Many mutations of the PIK3CA gene were found to increase enzymatic activity of PIK3CA, activate the AKT signaling, and allow growth factor-independent growth, invasion, and metastasis of cancer cells , Kang et al 2005, Samuels & Ericson 2006. Two PIK3CA mutational 'hotspots' were found in exons 9 and 20 and activating mutations in these regions were seen in many human cancers , Hayes et al 2006, Karakas et al 2006, Kozaki et al 2006, Phillips et al 2006, Qiu et al 2008, Santarpia et al 2008. Genetic amplification of the PIK3CA gene was also seen in many tumors, including ovarian cancer (Shayesteh et al 1999), cervical cancer (Ma et al 2000), brain tumors (Hui et al 2001), non-small cell lung cancer (Massion et al 2002), squamous cell carcinoma (Woenckhaus et al 2002), gastric carcinoma (Byun et al 2003), esophageal adenocarcinoma (Miller et al 2003), thyroid tumors (Wu et al 2005), oral squamous cell carcinoma (Kozaki et al 2006), head and neck squamous cell carcinoma , and anal squamous cell carcinoma (Patel et al 2007).…”