Head and neck squamous cell carcinoma (HNSCC) poses a major health problem in the world with approximately 600 000 new cases yearly. Treatment resistance is a major problem within this patient group and despite advances in treatment strategies the overall survival rate has unfortunately not increased.

One of the major components of the tumor microenvironment is the cancer associated fibroblasts (CAFs) which can modulate the treatment sensitivity, tumor growth, and the invasive potential of tumor cells.

The aim of this thesis was to identify predictive markers for treatment response in HNSCC and to study the crosstalk between tumor cells and CAFs that may underlie treatment resistance.

In paper I, we identified gene expression differences between one cisplatin sensitive cell line and two cisplatin resistant cell lines, by microarray analysis, and found that a high expression of matrix metalloproteinase (MMP) -7 was associated with resistance to cisplatin. In paper II, the epidermal growth factor (EGF) receptor ligands EGF, amphiregulin, and epiregulin were evaluated regarding their potential use as predictive biomarkers for cetuximab treatment response in tongue cancer cell lines and it was shown that EGF may serve as a marker for poor cetuximab response. In paper III and IV, we investigated the influence of CAFs on the proliferation, migration, gene expression, and cetuximab response of tumor cells. It was found that CAFs induced resistance to cetuximab in a MMP-dependent manner. In addition, a microarray analysis, comparing tumor cells co-cultured with CAFs and tumor cells cultured alone, revealed that CAFs induced multiple gene expression changes in tumor cells some of which are related to epithelial to mesenchymal transition. Some of these changes were found to be dependent on cell-cell contact.

Taken together, we here suggest MMP-7 and EGF to be predictive markers of cisplatin and cetuximab response, respectively. We also show that CAFs protect HNSCC cells from cetuximab treatment; however, the factor responsible for the protective effect is yet to be discovered.