Pietruszewka et al. found an elevated expression of MMP1 and MMP2 in immunohistochemical studies of tumors in advanced clinical stages (TNM/AJCC 3 and 4) of HNSCCs [152], similarly to De Carvalho et al. and Zhang et al., in which the overexpression of MMP9 was related to tumor recurrence, lymph node metastasis, and the development of second primary cancers [153,154]. The gene discussed is MMP9; the disease is neoplasm.