Combining dentistry and pathology to diagnose and treat oral cancer

Oral and maxillofacial pathologists are dentists by degree qualification and take a further training programme and FRCPath examination that is similar to their medically qualified colleagues. Their dentistry background provides them with in-depth knowledge of the complex processes that are involved in the development of teeth. Here, Dr Gillian Hall describes an unusual case of a tumour arising from the lining of a dental cyst.

I am sure that most people will be aware of the troubles that teeth can cause, but may not know that cellular remnants and clusters of residual cells from tooth formation lay dormant in our jaws, and have the ability to wake up, proliferate and form lesions in later life. These include common cysts, which occur around unerupted/partially erupted wisdom teeth and inflammatory cysts that appear around the roots of teeth that have been traumatised or are decayed. These lesions form much of the daily work of an oral and maxillofacial pathologist and are resolved when the tooth causing the problem is removed or if tooth-saving dental procedures are performed.

In some cases, a sample of tissue is taken and sent to us for diagnosis. Occasionally, the clinical and radiological appearances may not be entirely typical or explainable as one of these common cysts, and pathological examination of the tissue is essential. Whatever the scenario, we examine the tissue cells using a microscope, searching for evidence that might signify a more worrying diagnosis, namely one of the rare types of tumours that these cells have the capability to form.

In more than a dozen years as a consultant, this is the first time that I have seen a carcinoma arising in [a dental cyst] and likely the last.

Considering that these cluster of residual cells are present within the jaws and the soft tissues of the gums as scattered groups of rarely more than ten cells, the diversity of appearances of the lesions that they can become is astonishing. The most recent 2022 WHO publication lists 11 types of cyst, 16 benign and seven malignant tumours. In the UK population, less than 6% of tumours that develop in the tissues responsible for tooth formation are malignant and the less worrisome cysts are at least five-times more common than all the benign and malignant tumours combined.

In late 2021, tissue was submitted for diagnosis of a white growth that was seen on the gum of a 59-year-old woman, behind her last standing lower molar tooth. She did have a past history of tobacco use, so she could be considered as at risk from oral cavity cancer.

An urgent biopsy was performed. When I examined the tissue under the microscope, I could see that the squamous epithelial cells (the cell type that forms the lining of the mouth) weren’t typical. From this investigation, it wasn’t possible to show there was invasive growth, which would have indicated a diagnosis of cancer.

In the UK population, less than 6% of tumours that develop in the tissues responsible for tooth formation are malignant…

The clinical appearances were, however, highly suspicious, and there were features of concern in the bone that were visible after examination using radiography. To complicate matters, the scans revealed a buried wisdom tooth immediately below the abnormal area around which was a sizable cyst.

A limited surgical removal of the lesion would be considered the ideal treatment, but the presence of the tooth and cyst meant this was not possible. A full thickness segment of the jaw, to include the lesion, buried tooth and cyst was removed.

The macroscopic appearances after slicing the segment using a bandsaw suggested an inseparable relationship between the proliferative lesion on the gum and the cyst, which encased the unerupted tooth. Examination of slides showed the lesion to be a cancer that had arisen from the lining of the cyst.

…our job is to provide the precise diagnosis, thus give clarity to the patient and their clinical team and to inform the right course of treatment.

The reported incidence of the tumours that arise from the previously described tooth-forming cell clusters is 0.5 per 100,000, which in the current UK population would be 350 cases per year, and if less than 6% are cancerous, then this would amount to just 21 per year nationally.

The tumour was low grade and cut out with good margins to ensure no tumorous cells were left. There were no aggressive features and no spread to the lymph nodes of the patient’s neck. The prognosis for this patient based on these findings is excellent and no chemotherapy or radiotherapy was needed.

Before the reader dashes for an emergency trip to the dentist to check their wisdom teeth, it should be noted that I probably see a dozen dental cysts or more every week. In more than a dozen years as a consultant, this is the first time that I have seen a  carcinoma arising in one (and likely the last).

Dentists are always on the lookout for soft tissue growths and check for abnormalities on X-rays that could indicate the presence of a dental cyst or tumour, and will refer to a specialist when something is amiss.

Likewise, the histopathologist, whatever their background, is forever looking for that once in a career rarity that makes our job so fascinating. But, far more importantly, our job is to provide the precise diagnosis, thus give clarity to the patient and their clinical team and to inform the right course of treatment.