Oral tumours

Tumours associated with the oral cavity and pharynx account for 6% of all tumours in dogs and 3% of all tumours in cats, and tumour types and their associated behaviour differs between these two species (Findji, 2015); the World Small Animal Veterinary Association (WSAVA) global veterinary dentistry guidelines estimated that oral tumours account for 7% of all tumours in dogs and 10% in cats (Niemiec et al, 2017). In literature the incidence differs between authors, but the consensus seems to be between 3 and 10% of all dogs and cat tumours are orally-related. Dental, maxillofacial and oropharyngeal tumours often require a multimodal approach to their treatment, involving one or more of surgery, radiotherapy, chemotherapy and immunotherapy (Findji, 2015). It is important that veterinary professionals are aware of these different types of tumours their canine and feline patients may develop, including details regarding their behaviour and potential treatments, in order to educate clients and provide them with accurate information on which to make an informed decision about their pet's future. They know their pets best and ultimately are their advocates, so the extensive knowledge they have about their pet and its abilities, tolerances and idiosyncrasies needs to be combined with the clinical knowledge from the veterinary professional to decipher what is going to be the best course of action for that individual animal; with a focus on quality of life not longevity. Earlier detection and diagnosis of oral tumours provides the greatest chance for optimal recovery.

Tumour types and behaviour

A tumour is defined as an abnormal growth or swelling (Niemiec et al, 2017), and oral tumours are either malignant or benign and are of odontogenic (arising from tissues that give origin to teeth) or non-odontogenic (any other oral tissues) origin. It is important that veterinary professionals examine all of the tissues within the oral cavity during a physical examination including the teeth, gingiva, all surfaces of the oral mucosae, lips, tongue, sub-lingual areas and right back to the pharyngeal tissues, which will require the patient being compliant with having its mouth opened. It is important to appreciate the appearance of normal, healthy oral tissues so any abnormalities can be confidently identified, which can range from a seemingly innocuous erythematous area of tissue fairly similar in appearance to gingivitis, to large ulcerated and quite obvious masses. Clinical records must be precise with relation to the location of any abnormal tissues (Ostermeier, 2013), so it is not acceptable to simply record ‘gingival mass right mandible’, rather it should be ‘gingival mass at mesial aspect of 409’. Any abnormal appearing tissue within the oral cavity should be biopsied and analysed to discover its type (Lommer, 2013). Table 1 provides definitions of the different tumour types discussed in this article. In dogs there are a number of oropharyngeal tumours which are malignant, and these include:

• Malignant melanoma (MM), reported to make up 31–42% of all cases (Findji, 2015)
• Squamous cell carcinoma (SCC), reported to make up 17–25% of all cases (Findji, 2015)
• Fibrosarcoma (FSA), reported to make up 7.5–25% of all cases (Findji, 2015)
• Osteosarcoma (OSA), reported to make up 16–18% of all cases (Findji, 2015)
• Odontogenic tumours are also relatively common, but their frequency is difficult to estimate because they are often termed ‘epulides’, which is very non-descript and simply advises that the patient has localised gingival swelling (Findji, 2015; Niemiec et al, 2017). So, some of these could be malignant and some benign, but many are removed and disposed of without us ever discovering their true type because, as stated by Niemiec et al (2017: 53), ‘the term ‘epulis’ has been misused for decades as the description of a benign oral growth’.

In cats, SCC make up 75% to 80% of all cases and FSA between 13 and 17% of all cases of oral tumours (Bacon, 2012; Findji, 2015).

From a benign tumour perspective, gingival hyperplasia (GH) is common in dogs, less so in cats, and primarily occurs due to the host's response to plaque accumulation (Ostermeier, 2013). Ostermeier (2013) described a wide variety of presentations for GH lesions, both grossly and histologically, and it is often coupled with varying degrees of periodontal disease due to the pseudopockets created by the hyperplastic tissue. However, neoplasia will always be a potential differential diagnosis for the veterinary surgeon so it is advised that samples are sent for histopathological analysis to confirm they are benign. Eosinophilic granuloma complex is common in cats consisting of eosinophilic granuloma, eosinophilic ulcers and eosinophilic plaques occurring simultaneously in the same animal (Bonello, 2013). These lesions can involve the oral mucosa, palatal mucosa and the base of the tongue, which often results in the cats being dysphagic with associated ptyalism, and Bonello (2013) described them as histologically resembling a foreign body reaction. They can be medically managed or surgically excised, and veterinary professionals must be mindful that reports of these chronic ulcers transforming into SCC do exist, despite this being rare; therefore biopsy and histopathological examination is always advised (Bonello 2013).

A recent study by Wingo (2018) looked retrospectively at the prevalence of various histopathological diagnoses from oral lesion samples in 403 dogs and 73 cats; it found that in cats 51% were inflammatory in origin, 3% were odontogenic, and 47% were malignant neoplasms. Of the malignant neoplasms, 37% were SCC. In the dogs it was found that 28% were inflammatory in origin, 34% were odontogenic, and 30% were malignant neoplasms; of the malignant neoplasms the four most common were SCC at 7%, FSA at 6%, and MM and OSA both at 4.7%.

Different tumour types behave in different ways, and their behaviour influences the recommended treatment plan. Malignant oral tumours tend to be locally aggressive, therefore local disease control is extremely important and the long-term outcome for a patient is determined by the control the veterinary surgeon can achieve. Due to this locally aggressive behaviour, surgical intervention is considered to be the most important treatment modality (Knaake, 2012; Farese, 2014; Findji, 2015). Many malignant oral tumours metastasise relatively infrequently compared with tumours affecting other body systems, however MM and tonsillar SCC are the exception to this and do metastasise frequently (Findji, 2015). Table 2 provides an overview of the typical behaviour of the malignant tumour types described earlier (Findji, 2015).

Staging and diagnosis

Oral tumours tend to be identified during routine checks of patients, for example during a pre-vaccination health check, a pre-operative health check, during a veterinary nurse consultation, or perhaps when the animal is under general anaesthetic for a different procedure. If tumours are rostrally located then they tend to be identified earlier by the veterinary professional or the owner because they are much more visible and obvious (Farcas et al, 2012; Farese, 2014; Findji, 2015). If an owner has not identified a tumour they may present their pet to the veterinary practice because of other associated clinical signs, such as: bleeding originating from the tumour; halitosis, especially if there is an element of necrosis or the location of the tumour is providing a place for foodstuffs and oral bacteria to reside; hyperptyalism if the tumour is impacting the patient's ability to swallow saliva in a normal way; and dysphagia, which would typically be associated with a fairly sizeable tumour (Findji, 2015).

It is inadvisable to progress straight to surgery in these patients, and instead it is recommended the veterinary surgeon makes plans to achieve a definitive diagnosis of the tumour type before then planning surgical intervention (Findji, 2015). It is essential to know the type and nature of any tumour in order to achieve the best long-term results. Reaching a diagnosis would involve one or more of the following:

• Radiography (tumour): radiographs of the skull (lateral/dorsovental/ventrodorsal) may prove useful, including open-mouth views, however intra-oral images are preferred as the former views generally underestimate the degree of bone involvement (Knaake, 2012; Findji 2015). Holmstrom et al (2013) and Zacher and Marretta (2013) all advised that radiography is essential for the accurate evaluation and diagnosis of oral tumours, and Holmstrom et al (2013) supported their point by citing two previous studies where 27.8% of dogs and 41.7% of cats that presented with no abnormal findings on initial examination proved to have important pathology on radiographic evaluation, and in patients where abnormal findings were evident on initial presentation 50% of the dogs and 53.9% of the cats had additional pathology revealed by the radiographs. These two previous studies were both undertaken in 1998 by Verstraete et al and involved 115 cats and 226 dogs, respectively (Verstraete et al, 2018a, 2018b), so it would be beneficial to repeat them to update and increase the knowledge-base, however, no matter their age, both studies highlight the importance of intra-oral radiography in these cases.
• Computed tomography (CT) or magnetic resonance imaging (MRI): these imaging modalities are much more reliable than radiography and can provide the veterinary surgeon with much more accurate information regarding the location and extent of the tumour (Knaake, 2012). These modalities prove invaluable when it comes to surgical resection planning and also in cases where radiotherapy is going to be used, where accurate application of the radiation is essential (Findji, 2015).
• Fine needle aspirate (FNA) (tumour): these can be useful however the results may be affected where there is secondary inflammation or infection. They are also limited due to the fact that there is marked anaplasia of many oral tumour cells, which means the cells of a tumour have started to revert back to an immature or less differentiated form, which makes them less distinguishable from surrounding cells (Findji, 2015).
• Surgical biopsy: this is preferable to performing a FNA, and large, deep incisional or core biopsies, including some of the underlying bone where appropriate, are recommended. Zacher and Marretta (2013) advised obtaining multiple biopsies from different parts of the tumour to send for histopathological examination. The veterinary surgeon will take care when obtaining this biopsy to ensure the sample is not just the necrotic, inflamed or infected parts of the tumour, and they will also be mindful of their approach when accessing the tumour to ensure there is no seeding of tumour cells into adjacent/surrounding tissues. The last thing the veterinary surgeon wants as a result of the biopsy is to compromise the potential success of subsequent, definitive surgeries (Findji, 2015). Holmstrom et al (2013) advocated taking a biopsy of all abnormal masses visualised grossly or radiographically, but added that these should be sent for histopathological examination by a pathologist who is specifically qualified in oral tissue analysis. Bellows (2013) discussed the use of surgical lasers for excisional or incisional biopsies of oral masses, suggesting this method helps to control bleeding and improve visualisation (Figure 2)
• FNA (lymph nodes): this is recommended as the size of a lymph node is generally an unreliable indicator of nodal metastases, so even those that appear to be normal in size when compared with a healthy patient's nodes may indeed be affected (Findji, 2015).
• Radiography/CT (thorax): another step of the staging process where malignancy is suspected would involve imaging of the thoracic cavity. Thoracic radiographs may be obtained, however CT is much more sensitive and can also incorporate scanning of the mandibular, retropharyngeal and cervical lymph nodes at the same time (Knaake, 2012; Findji, 2015). Reiter (2013: 590) highlighted that CT ‘allows exploration of a large volume of soft and hard tissue in a significantly shorter examination time than magnetic resonance imaging’, and that with CT the ‘three-dimensional reconstruction images facilitate understanding of the overall picture’.

Treatment

The aims of treatment are to control the local disease and to control the potential systemic disease. Surgical intervention remains the main treatment modality for oral tumours, and if tumours are locally invasive then wide margins are required (Farcas et al, 2012; Farese, 2014; Findji, 2015). The main problems associated with surgical removal of tumours include the anatomical constraints associated with their location, and the availability of surrounding tissues to close tissue deficits post-excision for example (Farese, 2014). If the margins achieved during surgery are not ideal then adjuvant radiotherapy could be considered, and in cases of MM and tonsillar SCC, the use of systemic adjuvant treatments such as chemotherapy or immunotherapy are warranted due to their high metastatic rates (Findji, 2015). Farcas et al (2012) highlighted that surgery combined with either radiotherapy and/or chemotherapy for the treatment of oral and maxillofacial OSA has produced various outcomes in literature, and surgery remains the key intervention. Table 3 provides an overview of the different treatment modalities for oral tumours.

Survival times vary considerably depending on the tumour type, behaviour, how early it was diagnosed and the treatment performed. The prognoses in relation to survival times for the following tumour types are:

• GH: good following surgical excision, however local reoccurrence is possible (Ostermeier, 2013).
• Odontogenic tumours:
• Peripheral odontogenic fibroma (benign non-invasive) — good following surgical resection, but there is commonly reoccurrence following incomplete excision (Ostermeier, 2013). Wingo (2018) concurred, advising there is an excellent prognosis following surgical excision.
• Acanthomatous ameloblastoma (benign highly invasive) — good following complete excision, however if complete excision with adequate margins is not possible radiation therapy should be considered (Ostermeier, 2013). Wingo (2018) detailed a less than 5% recurrence rate following curative-intent surgical excision.
• MM: Wingo (2018) advised a guarded prognosis at best, with surgery and radiation therapy potentially providing good local control. The median survival time is reported to be roughly 23 months, however this is variable with Wingo (2018) outlining a patient with stage 2 MM of around 2 to 4 cm in diameter with no metastasis undergoing surgical treatment is likely to survive for typically around 6 months, however if they have lung metastases at the point of diagnosis survival is reported to be less, at around 131 days.
• SCC (dogs): Wingo (2018) reported, from available evidence, a 93.5% survival rate at 1 year post-curative intent surgery, with the range being typically a 19 to 26 month survival time. The adjunctive use of radiation therapy may potentially extend this time period, and prognosis is grave with no treatment.
• SCC (cats): long-term prognosis is poor without clean surgical margins, and survival at 1 year is around 9.5% (Wingo, 2018). If they are small lesions which can be surgically excised with clean margins combined with radiation therapy it can significantly extend survival times. There is a very poor prognosis if it is non-resectable or no treatment is initiated.
• FSA: there is a guarded prognosis for FSA. Wingo (2018) reported a mean survival time from literature of 488 days (maxillary), 301 days (mandibular) and 40 days (palatal). There is also evidence to support the fact that the size of the tumour impacts the average progression-free survival times, for example less than 2 cm is 45 months, less than 4 cm is 31 months, and greater than 4 cm is around 7 months (Wingo, 2018). Curative-intent surgery combined with radiation therapy, despite FSA typically being fairly radiation resistant, appears to be the best treatment option.
• OSA: Wingo (2018) reported from literature median survival times of 525 days, and there being differences in average survival times depending on the location of the tumours within the oral cavity: rostral tumours being 30 months, central tumours being 8 months, and caudal tumours around 5 months, so the worst prognosis is associated with the latter due to the problems surrounding being able to achieve wide surgical margins.

Patient care considerations

It is clear that dental, maxillofacial and oropharyngeal tumours can have a significant impact on the normal daily activities of an animal, more noticeably when the abilities to eat, drink and groom are considered. The anatomical and physiological dysfunction that can be caused by such tumours, depending on their extent and location, can result in animals struggling to perform all of these activities, and associated clinical signs such as eating less, dysphagia, weight loss, drinking less, and an unkempt coat are definitely ones their owners will notice even if they remain unaware of the tumour itself.

Fan (2014) discussed pain management in veterinary patients with cancer, and highlighted the fact that cancers are very capable of diminishing a patient's quality of life due to the pain they cause. The oral cavity is highly innervated and consequentially results in high pain levels experienced, therefore veterinary professionals should pain score animals before analgesics are given and repeat this assessment afterwards to establish the efficacy of the interventions. Fan (2014) also outlined that pain associated with cancer in human patients has been reported in literature to increase as the patient progresses towards death, so it is absolutely plausible that the same phenomenon occurs in veterinary patients. Fan (2014) explained that pain affects many bodily functions including cellular metabolism and immune system function, and made it very clear that all veterinary professionals must understand the pathophysiology of pain and the different types of pain in order to be able to recognise it in their cancer patients initially, but then to be able to formulate a multi-modal analgesic plan which incorporates both pharmacological and non-pharmacological interventions. Pharmacological interventions include the use of opioid drugs, non-steroidal anti-inflammatory drugs and adjuvant therapies, whereas non-pharmacological interventions include nutritional modifications, emotional enrichment and other complementary therapies such as acupuncture, massage, hydrotherapy, thermal therapies, electrical therapies (muscle stimulation/ultrasound/laser). The right combination of the above interventions where tolerated should be patient-specific with the analgesic plan tailored to their clinical signs and their actual or anticipated pain type and intensity. In a palliative care situation the veterinary nurse must support the owners as well as the patients, ensuring the owners are aware of clinical signs that might be indicative of pain or deterioration such as vocalisation, depression/withdrawal/reduced interaction, difficulty eating or anorexia, weight loss/loss of body condition, reduced or lack of water intake, pawing at the mouth area, and indeed recurrence of the lesion within the oral cavity.

Following surgical treatment of oral tumours, Zacher and Marretta (2013) suggested postoperative and ongoing care plans should involve the following considerations:

• Continued provision of intravenous fluid therapy until the patient is able to drink adequate volumes of water for themselves. Depending on the nature of the surgery it may take the patient a while to get used to drinking for themselves again, and pain must be managed well to avoid decreased water consumption and low grade dehydration ensuing, which can negatively influence their recovery.
• Similarly, the ability to eat will be affected to differing extents depending on the nature and extent of the surgery, so in many cases it is wise to place an oesophagostomy or gastrostomy feeding tube which can be utilised until the animal has fully regained this ability. Early enteral nutrition and planning for nutritional support prior to surgery is likely to benefit patients that are severely ill or are already debilitated, helping to improve patient outcomes (Frye et al, 2015).
• A soft food diet is indicated for 2 to 4 weeks for those patients where voluntary intake of food is possible straight after surgery.
• Chews and toys should be restricted until healing is complete, so this restriction will vary in length depending on the extent of the surgery and the patient's ability to heal in a timely manner; hopefully they will heal in an optimal timeframe without the addition of postoperative complications such as dehiscence, but the veterinary professionals must be mindful that often these patients are compromised prior to surgery as a consequence of the disease process and/or malnourishment, so may take longer to heal than a healthier patient.
• Revisits are essential to check healing and an initial check-up a couple of days post-surgery is advisable, with subsequent checks taking place 2 and 6 weeks after surgery, or more frequently if warranted.
• Adjunct oncological treatments such as chemotherapy, radiotherapy or immunotherapy should be performed as required, often once healing from the surgical intervention is complete.
• In cases where a malignant tumour was identified it would be prudent to examine the patient's surgical site and repeat chest radiographs or CT scans every 3 months, which can be extended up to 1 year between checks. The frequency of such re-examinations is at the discretion of the veterinary surgeon and should be based on the type, extent and behaviour of the tumour they diagnosed.
• Bacon (2012) described postoperative complications such as mandibular drift following a total mandibulectomy. The drift of the remaining mandible towards the midline due to the loss of normal anatomical occlusion can result in trauma of opposing tissues, for example the lower canine striking the tissues covering the hard palate, so the owner must be aware of the potential for further interventions should this occur in future and be problematic for the patient.

Conclusion

Oncology is a challenging area of veterinary medicine and when tumours, benign or malignant, affect the dental, maxillofacial or oropharyngeal tissues/structures the effects on the patient's health can be profound and the treatment potentially problematic. It is clear that a thorough examination and work-up using a variety of imaging modalities and diagnostic tests/tools is essential to assist the veterinary surgeon in reaching a diagnosis, and how thorough this process is will ultimately impact the quality of the planned treatment outcomes. The role of the veterinary nurse is of paramount importance in the management of such cases as regular pain scoring is indicated, assisted feeding is likely to be required to ensure adequate caloric intake for normal daily activities and healing, and careful monitoring of water intake is essential to prevent dehydration. It is important that the owners are fully informed about their pet's health status, diagnosis and treatment options before they make any decisions about their pet's future, and it is the responsibility of the veterinary professional to ensure the owner remains focused on quality of life as opposed to quantity of life.

KEY POINTS

• Sound knowledge regarding tumour types and their behaviour is vital when treatment planning.
• Veterinary professionals should consider referring such cases to specialists where possible if they do not have the required/ideal imaging or surgical facilities and equipment available to them.
• A holistic, multi-modal approach to treatment and nursing care is advocated and should be focused on improving quality of life and controlling associated pain.