Prognostic biomarkers in oral cancer: towards more individualized treatment

Abstract

In patients with oral squamous cell carcinomas (OSCC), the presence or absence of regional lymph node metastases in the neck is the most striking determinant for both prognosis and treatment planning. Adequate determination of the nodal status in these patients is therefore crucial. Unfortunately, current diagnostic imaging modalities (i.e. magnetic resonance imaging, computed tomography and ultrasonography with fine-needle aspiration of suspicious nodes) lack sufficient sensitivity to detect small nodal metastases. As a result, a significant amount of about 30% of patients with small tumors unsuspected for lymph node metastasis, the so-called early OSCC (clinically T1-2N0), has occult nodal metastasis. Therefore, new diagnostic modalities are needed to improve the accuracy of determining the nodal status and pave the road for a more individualized treatment. In this thesis, molecular diagnostics on epigenetic, genetic and proteomic level were used to find prognostic biomarkers with could predict the presence or absence of these occult nodal metastasis in early OSCC. A well-known epigenetic event in carcinogenesis is promoter hypermethylation of tumor suppressor genes (TSG), which could lead to the inability to transcribe the gene and subsequent expressional suppression of the TSG. Although no correlation between promoter hypermethylation and nodal metastases was found, patients with early OSCC with two or more hypermethylated genes had an improved (disease specific) survival. Besides epigenetic events, series of well-defined structural genetic changes play a major role in the carcinogenesis of OSCC, for example DNA mutations and copy number aberrations in both oncogenes and TSGs. In a pilot study, 1.977 genes were sequenced to find somatic mutations or mutational altered pathways which could trigger the primary tumor to metastasize. This so-called “cancer mini-genome” includes all up today known oncogenes, tumor suppressor genes, all kinases and important pathways related to carcinogenesis and anti-cancer treatment. This gave a good insight in the mutational landscape of early OSCC. However, no correlation between the mutational landscape of the cancer mini-genome and nodal metastases was found. Copy number aberrations (CNA) of 36 genes were analyzed using in a consecutive cohort of 164 OSCC, including 144 clinically early OSCC, to investigate their value as prognostic biomarker for occult nodal metastasis. Gain of chromosomal region 11q13 (CTTN, FADD, CCND1 and FGF4) had the strongest correlation with occult LNM, with a negative predictive value of 81%. A literature review with meta-analysis confirmed the correlation between amplification of CCND1 and the presence of nodal metastasis in OSCC. However, evidence as biomarker for occult nodal metastasis in early OSCC was sparse. Therefore, the correlation of amplification of CCND1 as well as protein overexpression of its encoding protein Cyclin D1 was confirmed and validated in a multicenter study in early OSCC. This revealed Cyclin D1 overexpression as the best prognostic biomarker for occult lymph node metastasis in early floor of mouth OSCC.