Written by Jonathan Clark
Australia has the highest incidence of cutaneous cancer in the world due to the combination of fair skin and high solar ultraviolet exposure. The incidence approaches three times the rate in North America and the United Kingdom. Skin cancers account for around 80% of all newly diagnosed cancers with two out of three Australians being diagnosed with skin cancer by the time they are 70. Non-melanoma skin cancers are so common that they not reported in cancer registries, however it is estimated that more than 750,000 people are treated for non-melanoma skin cancers in Australia each year. Of the reportable cancers, melanoma is the third most common cancer in Australians. Australia has the highest rate of parotid cancer in the world, the clear majority being metastatic cutaneous cancers to intra-parotid lymph nodes. As a result, 44% of all parotidectomies performed at the Sydney Head and Neck Cancer Institute are for metastatic skin cancer.
In 1988 Caldwell and Spiro reported the Memorial Sloane Kettering experience of 65 patients undergoing parotidectomy for metastatic melanoma. In this study 75% of patients undergoing elective parotidectomy for clinically positive neck disease had pathological involvement of parotid nodes and 43% had partial or total facial nerve sacrifice. Subsequently in 1991, O’Brien reported 998 patients treated for head and neck melanoma at the Sydney Melanoma Unit. A parotidectomy was performed in 148 patients and neck dissection in 397 patients. In 1994 O’Brien described a subset of 107 patients where superficial parotidectomy was used leading to a 96% facial nerve preservation rate without compromising local control. Both papers also provided evidence of improved local control with adjuvant radiotherapy (18.7% v 6.5%). It was recognised that the combination of parotidectomy with neck dissection was associated with a 40% marginal mandibular palsy rate demonstrating that ‘conservative’ interventions still had substantial inherent morbidity.
In 1991, Shah reported 111 patients undergoing radical neck dissection (80 therapeutic) for melanoma. He suggested that elective dissections could be selective, recommending that primary melanomas of the face, ear and anterior scalp undergo a parotidectomy and level I – IV neck dissection, whereas tumours of the posterior scalp and neck undergo a level II – V neck dissection. In this series, 36% of metastases ‘skipped’ the parotid. In 1995. O’Brien reported 106 elective dissections for primary melanoma with an 8% positivity rate, no survival benefit, and a 3% regional failure rate outside the predicted nodal drainage. The trials investigating the role of elective neck dissection by Veronesi (1977), Sim (1978), Balch (1996) had all demonstrated no improved survival. The morbidity of elective dissections combined with the unpredictable cutaneous lymphatic drainage and the absence of a survival advantage led to elective dissections being abandoned. In 1992, Morton validated the sentinel node concept in cutaneous melanoma based on intradermal blue dye. Around the same time, Norman (1991) demonstrated that most melanomas had three draining basins and 60% of these were unpredictable. O’Brien (1995) reported 97 patients undergoing sentinel node biopsy using lymphoscintigraphy with 50% having three or more sentinel nodes and 34% had unpredictable drainage.
The rate of nodal metastases in cutaneous squamous cell carcinoma (SCC) is considerably lower than melanoma, with less than 5% of head and neck cutaneous SCC developing parotid or cervical metastases (Brantsch 2008). This may increase up to 20% in primary cutaneous SCC with ‘high risk’ features such as large, thick or recurrent tumours, those with perineural invasion or lymphovascular invasion, or those located on the lip or ear. Whilst 70% of nodal metastases have extracapsular spread, the prognosis is more favourable in cutaneous SCC compared to melanoma (Bron 2003). Despite this, the rate of subclinical neck disease in patients with parotid metastases is approximately 30% in cutaneous SCC compared to 6% in melanoma, suggesting that treatment of the neck with surgery or radiotherapy is mandatory in cutaneous SCC but that the neck can be observed in melanoma. In 2005, Vauterin reported 93 elective neck dissections for patients with parotid metastases demonstrating that level II and III were involved in 89% and 32% of patients with subclinical neck disease, respectively. Indicating that many patients with parotid metastases from cutaneous SCC could be managed effectively by dissecting these levels alone. Despite the distribution of nodal metastases being clearly defined, the understanding of the prognostic impact of nodal disease remained rudimentary. The nodal (N) category in the 6th edition of the American Joint Commission on Cancer (AJCC) staging manual, grouped all metastases as N1 regardless of the size and number of nodes. In 2001, O’Brien questioned the adequacy of this system and proposed the P and N staging system for metastatic cutaneous SCC, providing local data to support this. Over several years this concept was developed and in 2006, Andruchow reported a multi-centre study of 325 patients from Australia, Canada and the United States demonstrating that immunosuppression, parotid (P) stage and neck (N) stage were independent predictors of survival.
- Whilst Professor O’Brien could not report this in his Semon lecture, the 7th Edition of AJCC staging manual in 2010 changed the staging of cutaneous SCC to incorporate the size and number of nodes into the N category.