Extending the role of the dental professional in the management of non-melanoma skin cancer

Non-melanoma skin cancer (NMSC) is the most frequently diagnosed malignancy worldwide and the incidence is on the rise.^1,2,3,4 In the UK, the rate of NMSC is 2.4 times greater than breast cancer, the next most frequent cancer.⁴ In fact, almost 152,000 cases of NMSC are diagnosed annually in the UK.⁵ Still, this is known to be a considerable underestimate attributable to under-reporting and inconsistencies in data collection.^2,5,6 The most frequent type is basal cell carcinoma (BCC) accounting for 75–80% of cases followed by cutaneous squamous cell carcinoma (cSCC) accounting for 15–20% of cases.^1,2 NMSC is most frequent in older age with a median age at diagnosis of 72 years in males and 74 years in females.⁶ The lifetime risk of developing BCC or cSCC is said to be 30% and 10%, respectively.^1,7,8 It is reported that over 80% of NMSC occur on the head and neck due to direct sun exposure, highlighting the important role of dental professionals in identification.^2,8,9

What is non-melanoma skin cancer?

BCC is a malignant skin cancer originating from the basal layer within the epidermis of the skin.¹ It is slow growing, rarely metastasizes (<0.1% incidence) and has a low mortality rate.^1,8,9,10 However, it is locally destructive, which may lead to significant morbidity.^2,10 Conversely, cSCC is a malignant skin cancer originating from keratinocytes within the epidermis.^4,11 There is a recognized risk of metastasis and therefore, a higher risk of morbidity and mortality when compared to BCC.^1,4,11 Despite this, death is still rare, and most NMSC is curable.² Various risk factors have been associated with the development of NMSC summarized in Table 1.

Clinical presentation

A routine dental examination involves a detailed and systematic extra- and intra-oral examination. According to the Faculty of General Dental Practice (FGDP), extra-oral examination should involve assessment of the face, head and neck including the assessment of any swellings and asymmetry.¹² The neck should be palpated for any abnormalities of the lymph glands or major salivary glands and the temporomandibular joint should be palpated at rest and during movement of the mandible. This systematic approach could be extended to a brief visual examination of the skin for suspected skin cancers. Considering approximately half the UK adult population see an NHS dentist, dental professionals are in a prime position to screen the head and neck for potential skin cancers in patients who may otherwise have no contact with a medical professional.¹³

Typical clinical presentations of a BCC include a pearly nodule with telangiectasis (prominent fine blood vessels) or an ulcer with raised rolled borders (Figure 1).^8,9 A BCC tends to remain asymptomatic, growing slowly over a period of months and years.³ A cSCC usually presents as an ulcer with a raised border or a red or hyperkeratotic scaly plaque with an indurated base (Figure 2).^3,4,9 Compared to a BCC, a cSCC tends to show more rapid growth, and may be tender to touch.³

Referral

The National Institute for Health and Care Excellence (NICE) guidance on ‘Suspected cancer: recognition and referral’ states that a suspected cSSC should be referred on the suspected cancer pathway (for an appointment within 2 weeks).¹⁴ Those with a suspected BCC should receive a routine referral unless there is concern that a delay may significantly impact the patient because of factors such as the site or size of the lesion. General dental practitioners may choose to refer the patient to their general medical practitioner or directly to their local oral and maxillofacial surgery department in secondary care. Ultimately, all NMSC of the head and neck should be treated in secondary care.⁶

Management

Diagnosis of NMSC is usually based on clinical features with histological confirmation following excision.^2,9,10 An incisional biopsy may be required in the event of diagnostic uncertainty, where a graft or flap will be required for reconstruction, anatomically complex areas like the nose, and also prior to radiotherapy.^2,4 NMSC may be staged using the tumour-node-metastasis (TNM) classification of malignant tumours.² Furthermore, NMSC may be assigned a ‘low risk’ or ‘high risk’ of recurrence.¹⁰ Around 5% of patients may present with high-risk features including locally advanced disease, close or positive margins, poorly differentiated histology, perineural invasion, recurrence and immunosuppression.^2,4,15,16 ‘High-risk’ patients should be managed by the skin cancer multidisciplinary team (MDT) within secondary care.^2,15 Currently, there are few randomized controlled trials to compare different treatment modalities for NMSC.^2,10 Treatment should be dictated by tumour-specific factors, including the type, size, location, depth of invasion and tissue margin, in addition to the patient's age, comorbidities and preferences.^10,17,18 Surgical excision is recommended for the majority of NMSC patients, particularly those with a low risk of recurrence.^2,16 However, where tumours cannot be fully resected, are inoperable, or the patient declines surgery, radiotherapy is the treatment of choice.^9,10 The mainstream treatments for NMSC are detailed in Table 2.

Surgery

Surgical excision aims to achieve complete excision of the tumour, in addition to a predetermined margin of normal skin (also known as a negative margin) to reduce the risk of recurrence.^10,11,19 The recommended margins for a BCC of <2 cm is 4–5 mm, low-risk cSCC >4 mm and high-risk cSCC >6 mm.^2,4

Mohs micrographic surgery is the staged resection and concurrent histological examination of the margin until complete clearance. It is recommended for high-risk NMSC, particularly BCCs, in cosmetic and functionally important sites, such as the eyelids, allowing maximum presentation of tissues.^2,10,11

Radiotherapy

Radiotherapy is the therapeutic use of high doses of ionizing radiation to control or kill malignant cells.²⁰ Radiation is typically delivered by either an external beam from a machine, such as an X-ray tube, or through the implantation of radioactive sources directly into the tumour. External beam radiotherapy is delivered by high-energy photons or electrons with energies in the range 10keV–20MeV with higher energies used to penetrate deeper into tissue.^10,18,19,20 For NMSC, superficial (low-energy) X-ray treatments are most commonly employed, but high-energy electrons and photons can be used in some situations.²

While surgery is the preferred primary treatment modality for NMSC, radiotherapy has been shown as an effective treatment option.^2,10,18,19 It may be used as a definitive treatment or an adjuvant treatment for high-risk NMSC following surgery to reduce the risk of recurrence where excision is incomplete and re-excision is not feasible.^{4,10,16,18,19} The tissue preservation with radiotherapy is particularly advantageous for NMSC of the midface where anatomical constraints, such as the medial canthus, lower eyelid or nose may hinder achieving a functional and cosmetic outcome.^2,18,19 Older people and those with severe comorbidities should also be considered for radiotherapy.^2,18,19 NMSC responds particularly well to radiotherapy, and when used as a definitive treatment, excellent local control is achieved. A study of 1021 cases of head and neck NMSC with no node involvement or metastasis managed with superficial energy external beam radiotherapy demonstrated local control at 5 years of 96% and 92% for BCC and cSCC, respectively.²¹

Radiotherapy of the target site with appropriate margins is precisely planned using computed tomography (CT).¹⁹ Megavoltage (MV) photon beams exhibit a skin sparing effect by delivering the maximum dose of radiation to deeper within the tissue once sufficient ‘build up’ has occurred from photon interaction. For a 6MV beam, this depth is approximately 15 mm. However, this is not always advantageous, and for cases where a high dose is to be delivered to a superficial target, a common practice is to place a layer of bolus, also known as ‘build-up’ material, over the target area to pull the maximum dose back up to the target depth (Figure 3).^22,23,24

A novel patient specific radiotherapy bolus

The ideal bolus material is water equivalent, of uniform thickness and density, with close adherence to the patient. Generic commercial sheets of flat pre-cut bolus are most commonly used. However, the curved and irregular surfaces of the head and neck may produce an ill-fitting bolus with air gaps, and a resultant discrepancy between the planned and delivered dose.²³ These limitations, commonly encountered by the radiotherapy physics team, were shared with a consultant in restorative dentistry who applied their skills in impression-taking and custom devices to produce a patient-specific bolus with close adaptation to the scalp.

Case

An 82-year-old male of European origin presented with a large and rapidly growing, fungating soft-tissue mass on the right frontal scalp (Figure 4). He was a retired office worker with fair skin and a family history of skin cancer.

A punch biopsy confirmed a diagnosis of moderately differentiated cSCC. Following an MDT discussion, surgical excision was performed, followed by reconstruction with a transposition flap and split thickness skin graft. Histological examination revealed a positive deep margin and a positron emission tomography (PET) scan picked up a 7 mm right level II node. The patient was staged at T3N1M0. The patient declined further surgery, and considering this was a high-risk cSCC, radiotherapy was planned to the scalp, right parotid and neck. The consultant in restorative dentistry took a plaster cast of the patient's scalp at the patient's CT simulation appointment. A customized bolus of 10 mm thickness with a locating tag over the patient's nose to ensure consistent positioning was produced. The initial acrylic prototype (Figure 5) revealed significant porosities (Figure 6), which led to the use of silicone to produce the definitive bolus (Figure 7). A CT scan taken with the silicone bolus in situ revealed a uniform thickness, density and close adherence to the scalp (Figure 8). A radiotherapy plan was devised indicating that a clinically acceptable dose was achieved at the scalp (Figure 9).

Conclusion

NMSC is the most common cancer in the UK and its prevalence is continuing to rise. Dental professionals play an important role in its identification and are encouraged to make skin cancer screening a routine part of the dental examination. This article highlights the importance of multidisciplinary working and how communication between specialities can result in innovation. The production of a novel patient-specific radiotherapy bolus has laid the foundations for its routine implementation in the management of NMSC of the head and neck and has opened the door to future multidisciplinary working. Further work is required to identify the practicalities of its implementation on a larger scale.