Underuse of the Sentinel Lymph Node Biopsy for High-Risk Squamous Cell Carcinoma of the Skin

Abstract

This study examines the underuse of the sentinel lymph node biopsy in the management of high-risk squamous cell carcinoma.

With recent changes in staging of cutaneous squamous cell carcinoma (SSC), we examine the underuse of the sentinel lymph node biopsy (SLNB) in the management of high-risk SCC. To date, the most important determinant of mortality in SCC is the presence of lymph node metastasis.¹ Recent data have led to an updated staging system for cutaneous SCC proposed by Brigham and Women’s Hospital, which emphasizes the presence or absence of high-risk features. This new staging system stratified T staging of SCC tumors based on the number of high-risk features present (>2-cm diameter, poor differentiation, perineural invasion, extension beyond subcutaneous fat). T1 tumors have no high-risk features, whereas T2a tumors have 1, T2b have 2 to 3, and T3 have all 4 or bone invasion. In a validation study by Schmitt et al,² tumors with 2 or 3 high-risk features had an SLNB positivity rate of 29%, whereas tumors with all 4 risk features had lymph node metastasis rate of 50%. The reported positivity rate of SLNB in the setting of high-risk SCC in the literature is 12% to 44%.³ The National Comprehensive Cancer Network guidelines recommend discussing and offering SLNB to patients with melanoma skin cancers of stages 1B and up.⁴ The SLNB positivity rate for stage 1B tumors is 7% to 10%, which is lower than that of high-risk SCC tumors.⁵

Methods

We created a database of all high-risk patients with SCC treated at the University of Southern California, including the Keck Medical Center and Los Angeles County Hospital in Los Angeles, California, from 2006 to the present time. Patient and tumor characteristics were documented, including treatment modality and whether SLNB was performed. Keck Medicine of the University of Southern California determined that institutional review board approval or human subjects committee approval and informed consent were not required for this retrospective study. All data were deidentified.

Results

With preliminary data results from our institution spanning from 2006 to present, less than 0.1% of all patients with high-risk SCC tumors underwent SLNB procedures. Alternatively, 14.0% underwent complete lymph node dissections. A little more than half (56.7%) of these complete lymph node dissections had microscopic tumor metastasis to local lymph nodes, whereas 43.3% of them were free of metastasis.

Discussion

Overall, we found prophylactic lymph node dissection to be overused and SLNB is underused in high-risk SCC. Given the cost and morbidity associated with prophylactic lymph node dissection, patients may benefit from a less invasive SLNB procedure before considering dissection. Limitations to SLNB include false-negative rates, particularly high for tumors on the head and neck because of alternate draining routes and bifurcating anatomy. Some view this as a contraindication for performing SLNB, but the use of single-photon emission computed tomography and preoperative lymphoscintigraphy can substantially decrease this false-negative rate.⁶ An uncertainty to be explored is the next step in the treatment of patients with SCC and positive SLNB results. Although lymph node dissection is recommended for patients with regional lymph node disease, no significant studies have determined whether this affects overall survival for patients with melanoma and nonmelanoma skin cancers. Further questions arise about whether SLNB should be performed in all high-risk patients with clinically N0 SCC. Currently, controversy exists in melanoma literature about whether to observe patients with clinical N0 disease or to perform an SLNB. Future prospective studies are needed to further elucidate the use of SLNB in SCC.