SPHK1 and metastatic malignant neoplasm in the lymph nodes: Univariate analysis for RFS showed that SPHK1 expression (p = 0.008; Figure 1D), tumor size (p = 0.009), depth of invasion (p = 0.049), lymph node metastasis (p < 0.001), and lymphovascular invasion (p < 0.001) were significant predictors of poor RFS (Table 2).