Prognostic significance of perineural invasion in vulvar squamous cell carcinoma

Background: Perineural invasion (PNI) is closely associated with poor survival in several types of malignant tumours, but whether this is true in vulvar squamous cell carcinoma (VSCC) is unclear. The aims of this study were to determine the prognostic significance of PNI in patients with VSCC. Patients and methods: We retrospectively analysed clinico-pathological data on 105 patients with VSCC (stages IB-IV) treated surgically at our medical center between 2005 and 2015. Results: PM was detected in 30 (28.6%) patients, and it was significantly associated with well-known clinical risk factors: large tumour size, depth of invasion, lymphatic vascular space invasion (LVSI), and intra- or extra-nodal spread. Significantly greater proportions of patients with PNI received adjuvant therapy after surgery (P=0.001) or showed local recurrence (P=0.002). Multivariable analysis indicated that risk factors for disease-free survival were tumour size (HR 3.02, 95%CI 1.75-7.75), LVSI (HR 4.82, 95%CI 1.36-17.07), depth of invasion (HR 3.11, 95%CI 1.50-6.44), lymph node metastasis (HR 3.15, 95%CI 1.14-8.96) and positive or close surgical margins (HR 4.86, 95%CI 1.67-14.19). The latter three variables were also risk factors for overall survival. PNI was associated with significantly shorter disease-free survival (DFS) (P=0.020) and overall survival (OS) (P=0.017) based on the log-rank test. Among patients who received adjuvant treatment, Kaplan-Meier curves indicated no significant differences between PM-positive or -negative subgroups in disease-free survival (P=0.085) or overall survival (P=0.061). Based on multivariable analysis of all patients, PM was not a significant risk factor for either type of survival. Conclusion: PNI in VSCC is associated with significantly shorter disease-free and overall survival, though it appears to be a weak independent predictor of worse prognosis. Combining PNI with other risk factors may be useful for predicting whether postoperative adjuvant therapy will be needed.