Tenascin and β6 integrin are overexpressed in floor of mouth in situ carcinomas and invasive squamous cell carcinomas
Introduction
Biologically, head and neck squamous cell carcinomas are a heterogeneous group of neoplasms. Clinical features, histologic appearances, susceptibility to etiologic factors, and survival rates vary from one anatomic region to another [1]. Carcinomas of the floor of the mouth have many features that support their distinction as a biologic subset of head and neck cancers. For example, the floor of the mouth is the intraoral site at greatest risk for development of in situ carcinoma [2], [3], [4], [5]. Precancerous lesions may exhibit a protracted preinvasive course, and the conversion rate to squamous cell carcinoma in this site is relatively high [6]. Preinvasive lesions have a high predilection for lateral spread into salivary excretory ducts without penetrating basement membrane [7]. Finally, floor of the mouth carcinomas exhibit an unusual invasiveness that is associated with a high incidence of occult metastases in early stage lesions [8], [9].
Tenascin is a glycoprotein that is up-regulated in processes that require keratinocyte movement, such as wound epithelization and connective tissue invasion by oral cancer cells [[10], [11], [12], [13]]. This extracellular matrix protein is formed at the epithelial–connective tissue interface and is thought to be produced by both keratinocytes and mesenchymal cells [14], [15]. Tenascin is also seen in peritumor tissue of lymph node metastases of oral squamous cell carcinomas [16]. In normal oral mucosa tenascin has been reported to be unexpressed or minimally expressed. Enhancement has been associated with increasing degrees of dysplasia, with the greatest intensity seen in invasive lesions, particularly at the advancing edge [17], [18]. These studies, however, have assessed tenascin expression in specimens from multiple oral sites with few floor of the mouth lesions included.
The integrin heterodimer, αvβ6, is a receptor for tenascin and is important in keratinocyte to matrix adhesion. The integrin subunit, β6, is exclusively expressed by epithelium, and is only evident during wound healing and carcinoma invasion [19]. Initial studies of oral cancers and dysplasias using frozen sections and antibodies to the dimer αvβ6 [13], [20] or to the subunit β6 [21] indicated new expression in these lesions. In a study of oral leukoplakias (not including floor of the mouth lesions and in situ carcinomas), only some dysplastic specimens stained positively for αvβ6. Outcomes for positively stained dysplasias, compared to negatively stained dysplasias, suggest that expression of this integrin may be predicitve of progression to carcinoma [20].
We hypothesized that tenascin and β6 integrins are overexpressed and co-localized in floor of the mouth in situ and invasive squamous cell carcinomas, and that these proteins are significantly enhanced as in situ carcinomas convert into invasive lesions. The purpose of this study was to assess and compare the expression of tenascin and β6 in floor of the mouth in situ and invasive squamous cell carcinomas by immunohistochemical methods.
Section snippets
Tissue specimens
Sequentially accessioned formalin-fixed, paraffin-embedded tissue blocks of normal mucosa, carcinoma in situ, and squamous cell carcinoma from the floor of the mouth were retrieved from the UCSF oral pathology archives. There were 20 in situ carcinomas, 16 of which had normal appearing epithelium (internal controls) in adjacent mucosa, and 20 invasive squamous cell carcinomas, 14 with normal appearing epithelium (internal controls) at specimen margins. The carcinomas were immediately flanked by
In situ carcinomas
Positive interface staining for tenascin was evident in all cases of in situ carcinoma of the floor of the mouth (Table 1; Fig. 1). In six cases staining was present in both the extracellular matrix as well as in adjacent basal keratinocytes. Staining was patchy in nine cases and continuous in the others. The 16 internal controls showed considerably weaker interface staining that was significantly different from in situ areas (P=0.0002). Normal external controls showed negative staining in four
Discussion
Squamous cell carcinomas of the floor of the mouth express a number of distinctive clinical and microscopic features that suggest they represent a biologic subset of head and neck cancer. In situ carcinomas occur relatively frequently in the oral floor, and their transition to invasive lesions represents a critical phase in tumor pathogenesis. Adhesion molecules expressed at the carcinoma–connective tissue interface must play a significant role in this process. Tenascin and its ligand, β6, have
Acknowledgements
This work was supported, in part, by NIDCR/NIH grant P50 DE/CA 11912-05.
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