SLPI and head and neck squamous cell carcinoma: In contrast to our own previously published data on SLPI in metastasized and non-metastasized HNSCC showing no correlation between the expression of SLPI and the degree of tumor differentiation (1), other researchers (29,30) demonstrated such a correlation in human epidermal tumors, leading to the hypothesis that SLPI protein levels represent a negative surrogate marker for tumor progression, thus corroborating our present data regarding SLPI expression and metastasis in HNSCC.