When we looked for genes upregulated in regrowing than “primary” tumors in a comparative pair-wise analysis, we found genes belonging to the extracellular matrix components (i.e. MMP9), to CSCs self-renewal maintenance (i.e. FOXP1), CSCs markers (i.e. CD44, PTPRC), and gene involved in MER-TK signaling pathway; the only downregulated gene was LIN28B. MMP9 mRNA expression was found enhanced in the ascites of chemoresistant ovarian cancer patients [42], and a recent meta-analysis indicated its positive association with poor prognosis in ovarian cancer [43]. The gene discussed is MMP9; the disease is ovarian cancer.