PIWIL1 and neoplasm: Expression of PIWIL1–2 has been investigated in various cancerous tissues [15]–[18], [21], [23], [35], but not MAEL, PIWIL3 and PIWIL4. Although the expression of PIWIL2 and 4 appeared high in tumor samples this was not significant, likely due to the fact that PIWIL2 and PIWIL4 were strongly expressed in normal ovarian tissues (Fig. 1B) and their expression among malignant tissues is highly variable.