Microsatellite Instability in Head and Neck Squamous Cell Carcinoma: A Study of a Brazilian Population

Squamous cell carcinoma (SCC) is the sixth most common solid tumor in the world. Apart from known risk factors for head and neck SCC (HNSCC), there is a lack of information about genetic susceptibility regions that may play pivotal roles in the tumorigenesis of these tumors. Therefore, we have aimed to analyze the presence of genetic instability in microsatellite markers distributed in the genome. Microsatellite instability (MSI) was found in 6 HNSCC patients, among which only one was detected by the D17S250 marker, whereas the other 5 occurrences (13.5%) were detected by the D3S1611 marker. No instability was found at markers D5S346, D10S197, D11S922, and D11S988. MSI detected by D3S1611 marker was present in 3 (14.3%) moderately differentiated tumors and in 2 (25.0%) poorly differentiated tumors, but no statistical significance was found. Genotypic frequencies for all markers showed no statistically significant distribution alteration, neither were they related to differentiation grade or patient age. Marker D3S1611 is located in the MLH1 gene, which is part of the mismatch repair system (MMR), helping to maintain genomic stability. We have found a higher rate of D3S1611 MSI in older patients, suggesting that this marker may be affected by aging processes in the DNA repair machinery. 1. Introduction Head and neck cancer is a significant cause of mortality and morbidity worldwide, presenting approximately 600,000 new cases yearly [1], whereas tumors of the oral cavity contribute with 389,000 new cases per year, with a mortality rate of 50% [2]. Squamous cell carcinoma (SCC) is the most common histological variant, comprising 90% of all cases [3]. SCC is the sixth most common solid tumor in the world [4], found preferentially in 50–70-year-old individuals [5]. Nonetheless, some studies point towards a frequency shift towards younger ages, with several cases in men with less than 40 years of age [6]. The epidemiology of head and neck SCC (HNSCC) shows tobacco, alcohol, and Human Papilloma Virus (HPV) infection as the most important risk factors, as well as genetic susceptibility [7–11]. Therefore, the search for genetic markers has increased significantly over recent years. Microsatellite regions are genomic 1–5？bp tandem repeats, generally noncoding, and the CA 2？bp repeat is the most common form [12]. These regions may present instability, especially caused by replication errors introduced by DNA polymerase, a phenomenon known as microsatellite instability (MSI) [13]. These replication mistakes may aid tumorigenesis through inactivation of tumor