Cancer-associated fibroblasts, a parameter of the tumor microenvironment, overcomes carcinoma-associated parameters in the prognosis of patients with mobile tongue cancer

Summary

Mobile tongue squamous cell carcinoma (MTSCC) is known for its strong propensity for regional metastasis and poor patient survival despite aggressive treatment, thus calling for new and reliable markers for predicting prognosis and guiding therapeutic management. Towards this end, three classes of markers were investigated: cancer-associated fibroblasts (CAFs; α-SMA positivity) as a representative of the tumor microenvironment, maspin (mammary serine protease inhibitor) as a tumor marker likely to be modulated by factors within the tumor microenvironment, and DNA content and Ki-67 labeling index as inbuilt tumor markers in 128 cases of MTSCC using immunohistochemistry and image cytometry. Of these markers, only CAF density was independently and relatively strongly associated with elevated mortality from MTSCC. The hazard ratio in the CAF-rich type of tumor microenvironment was 4.85 (95% CI 1.41–16.6, versus the CAF-poor) when adjusted by proportional hazards modeling for the center where the patient was managed, gender, tumor stage, presence of neck metastasis and age at diagnosis. CAF density was unrelated to non-MTSSC mortality. Given the strong association between increased CAF density and higher mortality in MTSCC, routine assessment of CAF density for disease course prognosis and inclusion as an integral part of treatment protocols are recommended.

Introduction

The incidence and death rates of cancers of the oral cavity and pharynx have slightly decreased over the past few decades,[1], [2] but the incidence of cancers of the tongue, oropharynx and tonsil are on the rise.¹ Furthermore, mobile tongue cancer is associated with poorer survival and a lower rate of local tumor control than other sub-sites with squamous cell carcinoma (SCC) of the head and neck region.³ This raises the possibility that mobile tongue SCC (MTSCC) is biologically distinctive⁴ and, as such, should be analyzed in separate prognostic studies, ideally, large-scale, multicenter and standardized ones.

Substantial evidence indicates that the development and progression of cancer not only depend on its genetic characteristics but also on interactions with its microenvironment, where tumor cells may alter the surrounding stroma and, in turn, stromal cells may promote cancer progression and acquisition of invasiveness.[5], [6] Cancer-associated fibroblasts (CAFs) are an excellent example for the sequel of the former and the executive of the latter. CAFs were shown to have emerged concomitantly with SCC cells in both an animal model of tongue carcinogenesis⁷ as well as in humans.⁸ Their overall distribution within the tumor microenvironment (TME) was found to be related to disease recurrence.⁹ A preliminary study on tongue SCC (without specifying whether it was mobile or base of tongue) reported that overall survival was related only to CAFs located at the invasive front but not to CAFs distributed throughout the entire tumor stroma.¹⁰ The presence of CAFs in the TME of metastatic lymph nodes of MTSCC, in addition to their pair-matched primary tumors, further emphasizes the essential role that CAFs play in tumor growth, invasiveness and spread.¹¹

Maspin (mammary serine protease inhibitor) is considered as being a tumor suppressor factor that increases cell adhesion and apoptosis, and decreases motility, angiogenesis and pericellular proteolysis.¹² The clinical contribution of maspin in cancer progression and metastasis is complex and seems to be the product of a number of factors, such as the genetic background of the tumor, type of cancer, expression of maspin (or lack of it) in the normal counterpart tissue and subcellular distribution. Furthermore, it has been shown that changes in the expression of maspin are modulated by cancer-associated inflammation and its mediators.[13], [14] Associations between the expression of maspin and clinical outcomes of patients with MTSCC are equivocal.[15], [16]

In this study, a relatively large series of MTSCC patients was assembled from two centers. We investigated the density of CAFs (α-SMA positivity) in the TME, maspin (a tumor marker liable to be modulated by factors within the TME), and the DNA content and Ki-67 labeling index (each an inbuilt tumor marker), and analyzed the association of these factors with mortality from MTSCC and from other causes of death.