Abstract
There is considerable variability in the reported incidence rates of perineural invasion (PNI) in oral squamous cell carcinoma (OSCC) and salivary gland malignancies (SGMs) worldwide. PNI exhibited by some OSCC and SGMs has been known as an independent predictor of poor prognosis and an indicator of aggressive behaviour. Furthermore, the literature suggests a possible molecular mechanism of PNI that results from a reciprocal interaction between tumour and nerve, probably due to some cellular factors and their respective receptors. A number of neurotrophic factors such as nerve growth factor (NGF) and its high affinity tyrosine kinase A (TrkA) receptor have been identified as being possibly of importance in PNI. The PI3K/Akt signalling pathway is a well-established driver of cancer progression, however, the mechanism of NGF-induced Akt phosphorylation remains unclear. Identifying the molecular background of PNI-driven OSCC and SGMs will shed light on the underlying pathogenesis and biological mechanism of PNI in cancer of oral cavity and salivary glands.Given the paucity of information on the role of these factors in OSCC and SGMs, this research was undertaken to help understand the mechanism of PNI in OSCC and SGMs. The proposed study involved a retrospective analysis of 132 and 14 archival formalin fixed paraffin embedded (FFPE) specimens from a cohort of 430 OSCC patients and 44 SGMs patients respectively. This study was conducted to establish the incidence of PNI and its impact on clinical outcomes of those patients who were diagnosed and treated in NHS Tayside, Scotland. Thereafter the samples were tested for the presence and pattern of NGF and TrkA expression by immunohistochemistry (IHC). Cell culture work investigating the role of Akt in NGF-induced cancer cell migration assays and signal transduction blocking assays was undertaken to study whether there is involvement of PI3K/Akt pathway in the molecular mechanism of PNI in OSCC and SGMs.
The study showed that the incidence of PNI was 17.4% in OSCC and 36.4% in SGMs. The vast majority of PNI-positive tumours in the cohort of OSCC and SGMs were tumours arising in the tongue and parotid glands respectively with a high incidence of PNI reported in Adenoid Cystic Carcinoma (AdCC) among the SGMs. With respect to PNI in OSCC there were multiple additional pathological factors that were significantly associated with it, including large tumour size, presence of nodal and extracapsular extension, increased depth and infiltrative pattern of invasion, poor tumour differentiation, advanced tumour front and lymphovascular invasion, while SGMs with PNI exhibited a greater potential only for lymphovascular involvement. PNI was associated with pain in OSCC and to facial nerve weakness in SGMs patients at the time of diagnosis, which may suggest that these symptoms could be a indicative of PNI in OSCC and SGMs. Interestingly, overexpression of NGF appeared to strongly influence pain perception in patients with OSCC and we can suggest that NGF might be a mediator of pain in OSCC.
There is a significant correlation between NGF/TrkA overexpression and PNI in OSCC tissue sections. Beside the tumour cells, the nerves in OSCC and SGMs sections expressed both NGF and TrkA. This suggests that there is a reciprocal interaction of tumours and nerves, in which NGF produced by tumour cells binds to TrkA receptors and may promote the growth and invasion of tumour via autocrine and paracrine actions leading to PNI.
The statistical analysis showed that the 5-year survival curve was significantly worse when PNI was observed in disease-specific survival (DSS) of OSCC and overall survival (OS), DSS and disease-free survival (DFS) of SGMs, therefore PNI can be used as an in indicator of poor prognosis in OSCC and SGMs. However, NGF and TrkA expressions were not related to the patient’s 5-years OS, DSS and DFS in both cohorts of OSCC and SGMs.
In addition, NGF stimulation has an adhesion, proliferation, scattering and migratory effect on OSCC and SGMs in-vitro with a morphological change from epithelial to mesenchymal-like phenotype which is a characteristic for invasive behaviour of tumours. NGF exerts these effects on OSCC and SGMs cells via its receptor TrkA by activating PI3K/Akt pathway and phosphorylates Akt at T308 and S473 leading to cell migration and potentially enhancing PNI. The addition of Akt inhibitor (MK-2206) blocks the NGF-induced OSCC and SGMs scattering and migration as well as the phosphorylation of Akt at both residues confirming the involvement of PI3K/Akt pathway in OSCC and SGMs that may offer a potential therapeutic approach in the future.
This study suggests that PNI is a predictive factor for tumour aggressiveness and poor prognosis in patients with OSCC and SGMs. It has also highlighted the potential of NGF and TrkA via PI3K/Akt pathway as reliable biological markers of PNI-related OSCC and SGMs.
| Date of Award | 2020 |
|---|---|
| Original language | English |
| Supervisor | Michaelina Macluskey (Supervisor), Ian Ellis (Supervisor) & Sharon White (Supervisor) |