The Value of Elective Parotidectomy in Advanced Squamous Cell Carcinoma of the Skin of the Head

Discussion

Lymph nodes of the parotid gland may be the main site of metastatic disease. These lymph nodes receive most of the lymphatic drainage from the ipsilateral facial skin and anterior scalp. They present a potential site for metastases in patients with CSCC, with a metastatic rate up to 10% (4, 8). About 40% of the metastases to the parotid gland are secondary to CSCC (9). This metastatic rate is especially true for immunocompetent patients with previously untreated tumors that are generally smaller than 1.5 cm in diameter at the time of first diagnosis. This relatively low incidence for regional metastases is opposed to the clearly higher metastatic incidence of so-called high-risk cancer.

The parotid metastases are in close neighbourhood to the cervical lymph nodes and are often associated with cervical lymph node metastases, similar to primary high-grade cancer of the parotid gland. Cervical metastases can be expected in more than 50% of the cases with parotid metastasis (10).

For defining patients at high risk for the development of regional metastases, several risk factors have been discussed in the literature. Primary lesion-specific risk factors include a tumor size of more than 1.5 cm, an infiltration depth of more than 4 mm, and low differentiation in tumor grading, as well as perineural tumor invasion. Patient-specific risk factors are an age of more than 70 years at diagnosis and immunosuppression (11-13). In the present study, half of the patients with metastatic disease suffered from chronic renal failure or were medically immunosuppressed because of renal transplantation. The impact of isolated risk factors or a combination of different risk factors on prognosis is still unknown.

The local tumor control rate, as well as the survival rate, of patients with parotid metastases from CSCC depends mainly on the size of the parotid metastases, and the infiltration of the facial nerve, and the skull base (6). Furthermore, the extent of cervical metastatic spread in the presence of parotid metastases has a high prognostic relevance. O'Brien et al. showed that patients with parotid metastases without cervical metastases, or with an isolated cervical metastasis of up to 3 cm have a 5-year survival rate of 65-70% while the 5-year survival of patients with multiple cervical metastases or metastases of more than 3 cm amounts to 30% (7). This and other studies confirm that the extent of parotid and cervical metastatic spread significantly influences the survival rate of the affected patients (14).

With this background, besides surgical treatment of CSCC, an early diagnosis and treatment of regional metastases is of significant importance. Similarly to benign tumors of the parotid gland, diagnosis of parotid metastases usually occurs when they reach a diameter of 2-3 cm. In particular, the early detection of occult lymph node metastases is thus clinically relevant.

The problem of the clinical N0 parotid and neck results from the partly insufficient sensitivity and specificity of non-invasive examination techniques. In head and neck cancer, if radiological examinations do not show any evidence of the presence of lymphatic spread, occult metastases must nonetheless be expected in approximately 25% of cases, depending on the location of the primary tumor (15). As yet, the incidence of occult parotid lymph node metastases has not been well-established and it is unclear whether performing elective parotidectomy and neck dissection is necessary in high-risk patients with N0 disease. There are only few studies in the literature about the incidence of occult parotid lymph node metastases. Yoon et al. reviewed 40 patients with CSCC of the auricle (16). In that series 8 out of 40 (20%) patients developed regional disease after excision of the primary tumor, which was localized in four cases (10%) in the parotid gland and in three cases (7.5%) in the neck. Therefore, the authors recommended elective parotidectomy with neck dissection with or without postoperative radiotherapy, especially in patients with poor prognostic features, such as cartilage invasion, extra-capsular growth, and depth of invasion, without setting any cut-off, and high histological grade. A former retrospective analysis of 11 patients with CSCC and eight patients with basal cell carcinoma of the auricle who underwent elective parotidectomy revealed no histological evidence of occult parotid metastases in all cases (17). The authors suggested that the risk of occult parotid metastasis from auricular carcinomas is low and that elective parotidectomy should not be considered mandatory in the surgical management of advanced auricular carcinomas. The low incidence of parotid involvement found in former studies is reflected in the results of the present study.

Currently, the most secure diagnostic procedure for detection of lymph node metastases is a histological examination by performing elective lymph node dissection. However, the increased sensitivity of such an approach may be associated with the potential risk of complications and an increased postoperative morbidity for patients, especially after elective parotidectomy. Although in the present study none of the patients suffered from facial nerve paralysis, in the literature, temporary facial nerve paralysis was documented in up to 42% and permanent paralysis in up to 3% of the patients after parotidectomy (18, 19).

In summary, elective parotidectomy, considering the potential risk of complications and morbidity and low rate of occult metastases, does not seem to be justified even in the case of high-risk CSCC. Frequent follow-up examinations, including sonography of the parotid gland and neck, should be performed, especially within the first 2 years after diagnosis in patients with risk factors in order to identify metastases at an early stage of disease (20).