Elsevier

Oral Oncology

Volume 36, Issue 6, November 2000, Pages 550-555
Oral Oncology

Exfoliative cytology of normal buccal mucosa to predict the relative risk of cancer in the upper aerodigestive tract using the MN-assay

https://doi.org/10.1016/S1368-8375(00)00051-8Get rights and content

Abstract

The high frequency of second or third primary tumors was first explained by Slaughter et al. with the concept of field cancerisation. Another theory postulates micrometastatic lesions as a reason for this phenomenon. The micronuclei (MN)-assay was evaluated to provide evidence for the concept of field cancerisation and to quantify the premalignant field change of normal mucosa in order to predict the individual cancer risk. MN-assay was carried out in 55 patients with squamous cell carcinoma of the head and neck, in 16 patients with a leucoplakia and in 99 healthy controls. A detailed questionnaire for population monitoring was completed. Buccal cytosmears of healthy mucosa of the study participants were examined for the MN count per 1000 cells. There was a direct correlation between tobacco abuse and increasing MN count as a sign of a cytogenetic damage of buccal mucosa cells. Alcohol did not influence the formation of MN. Both buccal sites were damaged in the same degree as proof of field cancerisation. The relative cancer risk (odds ratio) for smoking healthy controls with a definite MN frequency was estimated. Our study underscores the importance of the MN-assay as a biomarker to predict the relative cancer risk in the upper aerodigestive tract under suspicion of the individual susceptibility and the exposition to known carcinogenic agents such as tobacco and alcohol. The concept of field cancerisation was confirmed.

Introduction

Slaughter et al. [1] originally described the phenomenon of field cancerisation to account for their observation of multifocal squamous cell carcinomas in the upper aerodigestive tract. Second or third primaries develop in 7–30% of head and neck squamous cell carcinoma (HNSCC) patients [2], [3], [4], [5]. The main risk factor besides the individual-determined, endogenous susceptibility is the chronic abuse of tobacco and alcohol [6]. From a cell and molecular biological point of view cancer could be specified as a group of diseases, which are caused by certain changes in the genetic apparatus, first described by Boveri [7].

Current concepts suggest that malignant transformation is a result of defects in the oncogenes and tumor-supressor genes [8]. Nowadays cancer is known as the result of a multi-step process of genetic mistakes and changes, which lead through accumulation inside the cells to their degeneration [9], [10]. Renan statistically analyzed that six to 10 different persisting important genetic changes are required to create a malignant cell [11]. Despite multimodal therapies the survival rate of patients with HNSCC has not increased during the last decades. For the future the main research goal is to develop screening strategies indicating the individual cancer with certain biomarkers.

Biomarkers are instruments of individual tumor prevention and help to detect high-risk patients. They should allow statements concerning environmental and occupational exposition and further give information on the status of susceptibility. Biomarkers are divided in three groups: the first to define the exposure to carcinogenic agents, the second to show biological effects on the target tissue and the third to give information about the individual susceptibility [12].

In this examination the micronuclei (MN)-assay was used as a tool to estimate the individual risk of tumor diseases in the upper aerodigestive tract. Ideally, this biologic marker shows the degree of field cancerisation in the upper aerodigestive tract depending on the smoking and drinking habits of the examined person.

MN represent small, additional nuclei formed by the exclusion of chromosome fragments or whole chromosomes lagging at mitosis. MN rates therefore indirectly reflect chromosome breakage or impairment of the mitotic apparatus. The quantitative detection of MN is widely used for analysis of cytogenetic damage. Compared to the determination of chromosomal aberrations and sister chromatid exchanges an advantage of the MN test lies in the easier and clearly increased screening of chromosomal defects in cytological specimens [13].

The health significance of increased levels of MN is poorly understood and the aim of this study was to evaluate the MN-assay as a cytogenetic biomarker to predict the individual risk of HNSCC.

Section snippets

Materials and methods

From both buccal sides of the oral cavity, two cystosmears were taken of normal mucosa in 55 patients with squamous cell carcinomas and 16 patients with leucoplakias occurring within the upper aerodigestive tract. Smears were also taken from 99 healthy, age-matched controls. For each patient and control, a questionnaire for population monitoring was completed detailing age, sex, medical history, smoking and drinking habits and other carcinogenic/mutagenic agents, which influence cancer

Results

The characteristics of the study participants are listed in Table 1. The daily alcohol consumption is not presented in this table, because we did not find any relationship between daily alcohol intake and MN rate (P>0.05).

The mean MN values per cell were higher for specimens obtained from healthy buccal mucosa taken from patients with tumors or leucoplakias in the upper aerodigestive tract than from the abusing and non-abusing controls (P<0.001). The counts are demonstrated in Fig. 1.

Discussion

The measurement of the frequency of MN induced in cells by mutagen agents is widely used for analysis of cytogenetic damage. MN contain genetic material that is lost from the genome during mitosis, as a result of a clastogen or aneugen occurrence. Hence, there will arise bigger MN from whole chromosomes as a follow up to damaging of the spindle apparatus of the cell (aneugen). Smaller MN are the result of structural aberrations and consist of chromosomal fragments (clastogen) [15], [16].

For the

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