Background
TNM classification and grading only partially predict the prognosis of patients with oral squamous cell carcinomas (oscc) and cannot explain individual clinical courses of the disease. For the progression of oscc, genetic mutations which lead to dysregulation of embryonic signaling pathways [
1,
2] as well as immunologic factors play a significant role [
3,
4]. The phylogenetic highly conserved protein Galectin 3 (Gal3) is an important mediator between cell differentiation and tumor immunity [
5,
6] and contributes to the regulation of macrophage polarization [
7,
8].
Tumors and their precursor lesions often reveal alterations of Gal3 expression. Accordingly, a possible contribution of Gal3 to the pathogenesis of pancreatic, colorectal, liver and esophageal cancer could already be shown [
9]. There is evidence that Gal3 overexpression promotes malign transformation and metastatic spread [
10]. Cancer patients showed increased serum Gal3 and a correlation of Gal3 levels with prognosis was detectable [
10].
Evidence exists that Gal3 is also relevant for the progression of oscc. Some studies analyzed the role of Gal3 as prognostic factor especially in tongue cancer [
11‐
13]. One immunohistochemical study in patients with tongue cancer showed an association of Gal3 expression with dedifferentiation, metastases and poor prognosis [
12]. Another report examined the expression of Gal3 in a cohort of exceptionally young patients with oscc in several locations without identifying a correlation with tumor stage or grading [
14]. In addition to invasive squamous cell carcinomas, an increased expression of Gal3 could already be shown in precursor lesions of oral cancer [
6,
15].
Due to its contribution to the regulation of macrophage polarization (M1 vs. M2), Gal3 is an important immune modulator [
7,
8]. Macrophages are highly plastic cells involved in the formation of the tumor microenvironment and relevant for oscc prognosis [
16] and therapy response [
17,
18]. In this context M2 polarized macrophages contribute to immune tolerance and promote tumor progression and metastatic spread [
18,
19]. Gal3 can shift macrophage polarization towards M2 [
7].
Most studies analyzing Gal3 expression in oscc patients were performed in tongue cancer specimens and therefore only represent a subgroup of oscc. Gal3 expression in oscc was not yet analyzed in the context of a macrophage mediated immune-tolerant microenvironment in oscc. As an association of macrophage polarization with histomorphologic [
3] and prognostic parameters [
16] in oscc has already been shown, a comparative analysis of Gal3 and macrophage infiltration in oscc might elucidate an involved mediator.
Galectins like Gal3 are members of the lectins and are characterized by the ability to bind β-galactosides [
20]. Galectins have a phylogenetically conserved structure and are involved in cellular proliferation, survival, adhesion and migration [
20,
21]. With two functionally relevant protein domains, Gal3 is an unique member of the galectin family [
20]. It can interact with a variety of intracellular and extracellular proteins and is involved in the pathogenesis of fibrotic and malign diseases as well as in immune regulation [
20]. Gal3 can be detected in several human cells like immune cells and epithelial cells [
10].
Because of its high degree of phylogenetic conservation, its properties in carcinogenesis and regulation of macrophage polarization, Gal3 could be a prognosticator in oscc patients [
22,
23]. Moreover, as Gal3 inhibitors like citrus pectin are available, Gal3 could also be a target for molecular immune modulatory cancer therapy [
22,
23].
The current study aims to answer the question if Gal3 expression and the ratio of Gal3 positive cells vs. CD68 positive macrophages in diagnostic biopsies and tumor resection specimens of oscc is associated with histomorphologic parameters (T-, N-, L-, Pn-status, grading) of tumor progression.
Methods
Patients and tissue harvesting
A consecutively treated oscc patient collective was selected for this retrospective study. The patient selection was described in previous reports [
3,
24]. Biopsies and tumor resection specimens from a total of 34 patients histologically diagnosed with primary oscc were analyzed in this study. Tumor resection specimens from 34 patients and biopsies from 26 patients were available. The biopsies from nine cases were not available for analysis or too small for analysis. Because we counted macrophage infiltration in at least 1.1 mm
2 of carcinoma tissue, specimens with smaller carcinoma fractions were excluded. All patients were treated in 2011 at the Department of Oral and Maxillofacial Surgery of the University Hospital Erlangen. The study protocol was approved by the ethical committee of the University of Erlangen-Nuremberg (Ref.-No. 45_12 Bc). The specimens used in this study were obtained from tissue samples collected for routine histopathologic diagnosis. Each included specimen was judged to be a representative squamous cell carcinoma. In addition to the diagnosis of oscc, the following inclusion criteria were defined: pT1 or pT2 tumors, no restrictions in the grading of the tumor, no adjuvant preoperative radio- or chemotherapy and no distant metastasis at the time of diagnosis. Patients with former radio- or chemotherapy and pT3 and pT4 tumors were excluded. No study-related changes in the patients’ treatments took place.
The patient cohort (n = 34) consisted of 11 tongue oscc, 11 patients with a tumor of the floor of the mouth, 8 with alveolar crest carcinomas, 3 with a tumor of the palate and 1 of the cheek. The average age of the patients (23 males and 11 females) was 63 years. The pathohistological classified N-status was N0 in 19 cases and N+ in 15 cases (including all positive N-states). The histological grading was G1 in 2 cases, G2 in 26 cases and G3 in 6 cases. None of the patients in our cohort had distant metastases.
Immunohistochemical staining and quantitative analysis
The immunohistochemical staining procedure was performed as previously described [
3,
24]. The following primary antibodies were used: anti-Galectin 3 (sc-20,157, clone H-160, Santa Cruz, Dallas, Texas, USA) and anti-CD68 (11,081,401, clone KP1, Dako, Hamburg, Germany). An appropriate positive control was included in each series.
The tumor and biopsy sections were completely scanned and digitized using the method of “whole slide imaging”. The scanning procedure was performed in cooperation with the Institute of Pathology of the University of Erlangen-Nürnberg using a Panoramic 250 Flash III Scanner (3D Histech, Budapest, Hungary) in 40× magnification. All samples were digitally analyzed (Case viewer, 3D Histech, Budapest, Hungary). Quality controls were performed using a bright-field microscope (Zeiss Axioskop and Axiocam 5, at 100–400 × magnification).
For each sample, three visual fields showing the highest infiltration rate of positive cells were selected (hot spot analysis). The complete area of all three visual fields of one specimen was between 1.1 and 1.5 mm2 (Case viewer, 3D Histech, Budapest, Hungary).
Micrographs of the selected areas were imported into the Biomas analysis software (modular systems of applied biology, Erlangen, Germany) for cell counting. Two regions of interest were defined in the visual fields using the Biomas software: the epithelial tumor compartment and the stromal compartment.
A quantitative analysis was performed to determine the numbers of Galectin 3- and CD68-positive cells in the epithelial tumor compartment and the surrounding stroma. A Gal3 background staining, as it was visible in the epithelial tumor compartment of all cases, was not counted. Cells with strong Gal3 expression significantly surpassing the background expression of epithelial oscc tumor cells were counted as positive. Assessment of the cell density per mm
2 was performed as previously described [
16,
24].
Statistical analysis
To analyze the immunohistochemical staining, the cell count per mm2 was determined as the number of positive cells per mm2 of the specimen. Multiple measurements were pooled for each sample group prior to analysis. The results are expressed as the median and standard deviation (SD) and range. Box plot diagrams represent the median, the interquartile range, minimum (Min) and maximum (Max).
Two-sided, adjusted p-values ≤0.05 were considered to be significant. The analyses were performed using an ANOVA test with SPSS 22 for Mac OS (IBM Inc., New York, USA).
Acknowledgements
The authors thank Peter Hyckel for his contribution to the discussion and to the interpretation of the findings.
We thank Susanne Schoenherr and Elke Diebel for technical assistance. We also thank the dental students/research fellows Stafanie Queeney and Xiaoquin Lu for processing the tissue specimens, operating the immunohistochemistry autostainer apparatus and performing the cell counting.